Flame-retardant thermoplastic resin composition

ABSTRACT

The object of the present invention is to provide
         a flame-retardant thermoplastic resin composition, which comprises:   100 parts by weight of a thermoplastic resin (A),   0.1 to 30 parts by weight of a polyorganosiloxane-containing graft copolymer (B) obtained by polymerizing, in at least one stage, a monomer (B-3) comprising a polyfunctional monomer (B-2) containing at least two polymerizable unsaturated bonds within the molecule thereof, and/or a vinyl monomer (B-4) in the presence of polyorganosiloxane particles (B-1),   0.0005 to 5 parts by weight of at least one metal salt (C) selected from the group consisting of alkali metal salts and bivalent or further polyvalent metal salts, and   0.05 to 2 parts by weight of a fluororesin (D).

RELATED APPLICATIONS

This application is a nationalization of PCT Application No.PCT/JP03/05325 filed Apr. 25, 2003. This application claims priorityfrom Japanese Patent Application No. 2002-126918 filed on Apr. 26, 2002and Japanese Patent Application No. 2002-325870 filed on Nov. 8, 2002.

FIELD OF THE INVENTION

The present invention relates to a flame-retardant thermoplastic resincomposition.

BACKGROUND ART

Thermoplastic resins, in particular polycarbonate-based resins, arewidely used in or as electric/electronic parts, OA equipment, domesticarticles or building materials owing to their good impact resistance,heat resistance, and electric characteristics, among others. Whereaspolycarbonate-based resins have higher flame retardancy as compared withpolystyrene resins and the like, there are fields in which a stillhigher level of flame retardancy is required, mainly in the fields ofelectric/electronic parts, OA equipment, and the like. Thus,improvements in such flame retardancy have been attempted by addition ofvarious flame retardants. For example, the addition of organohalogencompounds and organophosphorus compounds is conventional in the art.However, most of organohalogen compounds and organophosphorus compoundshave a problem concerning toxicity and, in particular, organohalogencompounds have a problem in that, upon combustion, they generatecorrosive gases. Under such circumstances, the demand for halogen-freeand phosphorus-free flame retardants for rendering such resinsflame-retardant has been increasing in recent years.

The utilization of polyorganosiloxane compounds (also called silicones)as halogen-free, phosphorus-free flame retardants has been proposed. Forexample, Japanese Kokai Publication Sho-54-36365 describes thatflame-retardant resins can be obtained by kneading together a siliconeresin comprising monoorganopolysiloxane and a nonsilicone polymer.

Japanese Kokoku Publication Hei-03-48947 describes that mixtures of asilicone resin and a group IIA metal salt confer flame retardancy uponthermoplastic resins.

Japanese Kokai Publication Hei-08-113712 describes a method of obtainingflame-retardant resin compositions by dispersing, in a thermoplasticresin, a silicone resin prepared by mixing up 100 parts by weight of apolyorganosiloxane and 10 to 150 parts by weight of a silica filler.

Japanese Kokai Publication Hei-10-139964 describes that flame-retardantresin compositions can be obtained by adding a solvent-soluble siliconeresin having a weight average molecular weight of not less than 10,000but not more than 270,000 to a nonsilicone resin containing aromaticring.

However, the silicone resins described in the above-cited documents areeffective in conferring flame retardancy only to an unsatisfactoryextent. An increase in the amount of flame retardant for attainingsatisfactory results will cause deterioration in impact resistance ofthe resulting resin compositions and, thus, there is still a problemsuch that it is difficult to obtain resin compositions with bothexcellent flame retardancy and good impact resistance.

Japanese Kokai Publication 2000-17029 describes that flame-retardantresin compositions can be obtained by incorporating in a thermoplasticresin a composite rubber type flame retardant resulting fromgraft-polymerizing a vinyl monomer onto a composite rubber composed of apolyorganosiloxane rubber and a poly(alkyl (meth)acrylate) rubber.

Japanese Kokai Publication 2000-226420 describes that flame-retardantresin compositions can be obtained by incorporating in thermoplasticresins a polyorganosiloxane type flame retardant resulting from graftinga vinyl monomer onto composite particles comprising a polyorganosiloxanehaving aromatic group and a vinyl polymer.

Japanese Kokai Publication 2000-264935 describes that flame-retardantresin compositions can be obtained by incorporating in thermoplasticreins a polyorganosiloxane-containing graft copolymer resulting fromgraft polymerizing a vinyl monomer onto polyorganosiloxane particles notlarger than 0.2 μm in size.

The flame-retardant resin compositions described in Japanese KokaiPublication 2000-17029, Japanese Kokai Publication 2000-226420 andJapanese Kokai Publication 2000-264935 all have satisfactory levels ofimpact resistance but are not satisfactory in flame retardancy. Thus,they still have a problem in that they are not excellent both in flameretardancy and in impact resistance.

Further, while Japanese Kokai Publication 2000-264935 described that thepolyorganosiloxane-containing graft copolymer can be recovered in theform of a powder by spray drying, there is no specific example of thecomposition is given. As far as the investigation made by the presentinventors indicates, such a polyorganosiloxane-containing graftcopolymer as recovered by spray drying is good in flame retardancy buthas another problem, namely it is poor in powder characteristics ascompared with the grade of copolymer recovered by salt coagulation, inparticular it is unsatisfactory in anti-blocking property.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a flame-retardantthermoplastic resin composition which is halogen-free andphosphorus-free and excellent both in flame retardancy and impactresistance.

Another object of the invention is to provide a flame retardant forthermoplastic resins which is excellent in anti-blocking property andwill never impair the moldability, typically the thermal stability, ofthe resins.

As a result of intensive investigations made by the present inventors tosolve the problems discussed above, it was found that when a specificpolyorganosiloxane-containing graft copolymer and a specific metal saltand a fluororesin are combinedly incorporated in a thermoplastic resin,a flame-retardant thermoplastic resin composition excellent in bothflame retardancy and impact resistance can be obtained and a flameretardant for thermoplastic resins which is excellent in anti-blockingproperty and will never impair the thermal stability of the resins canbe obtained. Such and other findings have led to completion of thepresent invention.

Thus, the invention provides:

A flame-retardant thermoplastic resin composition, which comprises:

100 parts by weight of a thermoplastic resin (A),

0.1 to 30 parts by weight of a polyorganosiloxane-containing graftcopolymer (B) obtained by polymerizing, in at least one stage, a monomer(B-3) comprising a polyfunctional monomer (B-2) containing at least twopolymerizable unsaturated bonds within the molecule thereof, and/or avinyl monomer (B-4) in the presence of polyorganosiloxane particles(B-1),

0.0005 to 5 parts by weight of at least one metal salt (C) selected fromthe group consisting of alkali metal salts and bivalent or furtherpolyvalent metal salts, and

0.05 to 2 parts by weight of a fluororesin (D) (Claim 1);

The flame-retardant thermoplastic resin composition according to Claim1,

wherein the thermoplastic resin (A) is a polycarbonate-based resin,

the amount of the polyorganosiloxane-containing graft copolymer (B) is0.5 to 20 parts by weight per 100 parts by weight of thepolycarbonate-based resin,

the metal salt (C) is an alkali metal salt of a sulfur-containingorganic compound and/or a bivalent or further polyvalent metal salt of asulfur-containing organic compound and the amount thereof in total is0.001 to 5 parts by weight per 100 parts by weight of thepolycarbonate-based resin (Claim 2);

The flame-retardant thermoplastic resin composition according to Claim2,

wherein the metal salt (C) comprises both an alkali metal salt of asulfur-containing organic compound and a bivalent or further polyvalentmetal salt of a sulfur-containing organic compound (Claim 3);

The flame-retardant thermoplastic resin composition according to any oneof Claims 1 to 3,

wherein the bivalent or further polyvalent metal salt is an alkalineearth metal salt (Claim 4);

The flame-retardant thermoplastic resin composition according to any oneof Claims 1 to 4,

wherein the polyorganosiloxane-containing graft copolymer (B) isproduced by polymerizing, in at least one stage, 0 to 10 parts byweight, per 100 parts by weight of the whole copolymer, of a monomer(B-3) comprising 100 to 20% by weight of a polyfunctional monomer (B-2)containing at least two polymerizable unsaturated bonds within themolecule thereof and 0 to 80% by weight of another copolymerizablemonomer (B-5) in the presence of 40 to 95 parts by weight ofpolyorganosiloxane particles (B-1) and further polymerizing, in at leastone stage, 5 to 50 parts by weight of a vinyl monomer (B-4) (Claim 5);

The flame-retardant thermoplastic resin composition according to any oneof Claims 1 to 5,

wherein the polyorganosiloxane particles (B-1) has a volume averageparticle diameter of 0.008 to 0.6 μm (Claim 6);

The flame-retardant thermoplastic resin composition according to any oneof Claims 1 to 6,

wherein the polyorganosiloxane particles (B-1) are produced withoutusing any tri- or further poly-functional silane (Claim 7);

The flame-retardant thermoplastic resin composition according to any oneof Claims 1 to 7,

wherein the polyorganosiloxane particles (B-1) are in a latex form(Claim 8);

The flame-retardant thermoplastic resin composition according to any oneof Claims 1 to 8,

wherein the vinyl monomer (B-4) is such one that a polymer derived fromthat monomer alone has a solubility parameter of 9.15 to 10.15(cal/cm³)^(1/12) (Claim 9);

The flame-retardant thermoplastic resin composition according to any oneof Claims 1 to 9,

wherein the vinyl monomer (B-4) is at least one monomer selected fromthe group consisting of aromatic vinyl monomers, vinyl cyanides,(meth)acrylic ester monomers and carboxyl group-containing vinylmonomers (Claim 10);

The flame-retardant thermoplastic resin composition according to any oneof Claims 2 to 10,

wherein the sulfur-containing organic compound is at least one compoundselected from the group consisting of sulfonamides, (alkyl)aromaticsulfonic acids, perfluoroalkanesulfonic acids, aliphatic sulfonic acidsand diphenyl sulfone sulfonic acids (Claim 11);

The-flame-retardant thermoplastic resin composition according to any oneof Claims 2 to 10,

wherein the sulfur-containing organic compound is an (alkyl)aromaticsulfonic acid (Claim 12);

The flame-retardant thermoplastic resin composition according to any oneof Claims 1 to 12,

which further comprises not more than 2 parts by weight of anantioxidant (E) (Claim 13);

The flame-retardant thermoplastic resin composition according to Claim13,

wherein the antioxidant (E) comprises a combination of at least oneantioxidant having the isocyanuric ring structure within the moleculethereof and at least one other antioxidant (Claim 14);

A method of producing the flame-retardant thermoplastic resincomposition according to Claim 3,

which comprises:

emulsion-polymerizing, in at least one stage, a monomer (B-3) comprisinga polyfunctional monomer (B-2) containing at least two polymerizableunsaturated bonds within the molecule thereof, and/or a vinyl monomer(B-4) in the presence of polyorganosiloxane particles (B-1),

recovering the resulting polyorganosiloxane-containing graft copolymercontaining a bivalent or further polyvalent metal salt of asulfur-containing organic compound by the coagulation method, and

melt-kneading a thermoplastic resin (A), thepolyorganosiloxane-containing graft copolymer containing the bivalent orfurther polyvalent metal salt of the sulfur-containing organic compound,an alkali metal salt of a sulfur-containing organic compound, and afluororesin (D) together (Claim 15);

A flame retardant for thermoplastic resins,

which comprises:

a polyorganosiloxane-containing graft copolymer obtained bypolymerizing, in at least one stage, a monomer (B-3) comprising apolyfunctional monomer (B-2) containing at least two polymerizableunsaturated bonds within the molecule thereof, and/or a vinyl monomer(B-4) in the presence of polyorganosiloxane particles (B-1),

an alkali metal salt of a sulfur-containing organic compound, and

a bivalent or further polyvalent metal salt of a sulfur-containingorganic compound (Claim 16); and

A method of producing the flame retardant for thermoplastic resinsaccording to Claim 16,

which comprises:

emulsion-polymerizing, in at least one stage, a monomer (B-3) comprisinga polyfunctional monomer (B-2) containing at least two polymerizableunsaturated bonds within the molecule thereof, and/or a vinyl monomer(B-4) in the presence of polyorganosiloxane particles (B-1),

recovering the polyorganosiloxane-containing graft copolymer containinga bivalent or further polyvalent metal salt of a sulfur-containingorganic compound by the coagulation method, and

blending the polyorganosiloxane-containing graft copolymer containingthe bivalent or further polyvalent metal salt of the sulfur-containingorganic compound with an alkali metal salt of a sulfur-containingorganic compound (claim 17).

In the following, the present invention is described in detail.

DETAILED DISCLOSURE OF THE INVENTION

The flame-retardant thermoplastic resin composition of the inventioncomprises 100 parts by weight of a thermoplastic resin (A), 0.1 to 30parts by weight of a polyorganosiloxane-containing graft copolymer (B),0.0005 to 5 parts by weight of at least one metal salt (C) selected fromthe group consisting of alkali metal salts and bivalent or furtherpolyvalent metal salts, and 0.05 to 2 parts by weight of a fluororesin(D).

The polyorganosiloxane-containing graft copolymer (B), when incorporatedin the thermoplastic resin (A), improves the flame retardancy and impactresistance of the resulting moldings. In accordance with the presentinvention, the polyorganosiloxane-containing graft copolymer (B) is usedin an amount of 0.1 to 30 parts by weight per 100 parts by weight of thethermoplastic resin. At lower addition levels, neither flame retardancynor impact resistance will be manifested while excessively high levelswill unfavorably cause a deterioration in flame retardancy and alowering of thermal resistance against a temperature of the moldings.Preferably, the addition level is not lower than 0.5 part by weight,more preferably not lower than 0.7 part by weight, still more preferablynot lower than 1 part by weight. On the other hand, it is preferably nothigher than 20 parts by weight, more preferably not higher than 10 partsby weight, still more preferably not higher than 6 parts by weight, mostpreferably not higher than 4 parts by weight.

The above-mentioned polyorganosiloxane-containing graft copolymer (B) isobtained by polymerizing, in at least one stage, a monomer (B-3)comprising a polyfunctional monomer (B-2) containing at least twopolymerizable unsaturated bonds within the molecule thereof, and/or avinyl monomer (B-4) in the presence of polyorganosiloxane particles(B-1). It is preferably the product obtained by polymerizing, in atleast one stage, 0 to 10 parts by weight, per 100 parts by weight of thewhole polyorganosiloxane-containing graft copolymer (B), of a monomer(B-3) comprising 100 to 20% by weight of a polyfunctional monomer (B-2)containing at least two polymerizable unsaturated bonds within themolecule thereof and 0 to 80% by weight of another copolymerizablemonomer (B-5) in the presence of 40 to 95 parts by weight ofpolyorganosiloxane particles (B-1) and further polymerizing, in at leastone stage, 5 to 50 parts by weight of a vinyl monomer (B-4).

The polyorganosiloxane particles (B-1) preferably have a volume averageparticle diameter of not smaller than 0.008 μm, more preferably notsmaller than 0.01 μm, still more preferably not smaller than 0.1 μm, asdetermined by the light scattering method or by observation under anelectron microscope. That diameter is preferably not larger than 0.6 μm,more preferably not larger than 0.38 μm, still more preferably notlarger than 0.3 μm. While there is a tendency for the production of suchparticles having a volume average particle diameter smaller than 0.008μm to become difficult, particle diameters exceeding 0.6 μm tends tolead to deterioration in flame retardancy.

For the flame retardancy and impact resistance, the polyorganosiloxaneparticles (B-1) preferably have a toluene insoluble matter content(toluene insoluble matter content after 24 hours of immersion of 0.5 gof the particles in 80 ml of toluene at room temperature) of not higherthan 95%, more preferably not higher than 50%, in particular not higherthan 20%.

The polyorganosiloxane particles (B-1) of the invention conceptuallyinclude not only particles made of a polyorganosiloxane alone but alsomodified polyorganosiloxane particles containing up to 5% by weight ofanother (co)polymer. Thus, the polyorganosiloxane particles may containup to 5% by weight of poly(butyl acrylate) and/or a butylacrylate-styrene copolymer, for instance.

As specific examples of the polyorganosiloxane particles (B-1), theremay be mentioned polydimethylsiloxane particles,polymethylphenylsiloxane particles, anddimethylsiloxane-diphenylsiloxane copolymer particles, among others. Thepolyorganosiloxane particles (B-1) may comprise one single species or acombination of two or more species.

The polyorganosiloxane particles (B-1) can be obtained, for example, bypolymerizing (1) an organosiloxane, (2) a bifunctional silane, (3) anorganosiloxane and a bifunctional silane, (4) an organosiloxane and avinyl type polymerizable group-containing silane, (5) an organosiloxaneand a silane having a group capable of radical reaction, (6) abifunctional silane and a vinyl type polymerizable group-containingsilane, (7) a bifunctional silane and a silane having a group capable ofradical reaction, (8) an organosiloxane, a bifunctional silane and avinyl type polymerizable group-containing silane, (9) an organosiloxane,a bifunctional silane and a silane having a group capable of radicalreaction, or (10) an organosiloxane, a bifunctional silane, a vinyl typepolymerizable group-containing silane and a silane having a groupcapable of radical reaction, or by polymerizing such a monomer ormonomers with a tri- or further poly-functional silane further addedthereto. The term “bifunctional silane” means a silane in which thetotal number of hydroxyl group(s) and/or hydrolysable group(s) bound toa silicon atom is 2. The term “tri- or further poly-functional silane”means a silane in which the total number of hydroxyl group(s) and/orhydrolysable group(s) bound to a silicon atom is not smaller than 3.

The organosiloxane and bifunctional silane each is a componentconstituting the main framework of the polyorganosiloxane chain. Asspecific examples of the organosiloxane, there may be mentionedhexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4),decamethylcyclopentasiloxane (D5), dodecamethylcyclohexasiloxane (D6),tetradecamethylcycloheptasiloxane (D7), andhexadecamethylcyclooctasiloxane (D8). As specific examples of thebifunctional silane, there may be mentioned diethoxydimethylsilane,dimethoxydimethylsilane, diphenyldimethoxysilane,diphenyldiethoxysilane, 3 -chloropropylmethyldimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane,heptadecafluorodecylmethyldimethoxysilane,trifluoropropylmethyldimethoxysilane, andoctadecylmethyldimethoxysilane. Among these, 70 to 100%, preferably 80to 100%, of D4, mixtures of D3 to D7, or mixtures of D3 to D8 and 0 to30%, preferably 0 to 20%, of diphenyldimethoxysilane,diphenyldiethoxysilane and/or the like as the balance component arepreferably used from the viewpoint of the good economy and flameretardancy.

The vinyl type polymerizable group-containing silane or the silanehaving the group capable of radical reaction mentioned above is acomponent to be copolymerized with the above-mentioned organosiloxane,bifunctional silane, tri- or further poly-functional silane and/or thelike for the introduction of the vinyl type polymerizable group or thegroup capable of radical reaction onto side chains or a terminus of thecopolymer. The vinyl type polymerizable group or the group capable ofradical reaction serves as an active site for grafting on the occasionof chemically binding to the (co)polymer formed, as mentioned laterherein, from a monomer (B-3) comprising a polyfunctional monomer (B-2)containing at least two polymerizable unsaturated bonds within themolecule, and/or a vinyl monomer (B-4). Furthermore, it is a componentcapable of forming a crosslinking bond between active sites for graftingin the manner of radical reaction by the use of radical polymerizationinitiator, hence capable of being utilized also as a crosslinking agent.The radical polymerization initiator may be the same one as can be usedin the graft polymerization which is to be mentioned later herein. Evenwhen the crosslinking is effected by the radical reaction, some remainsas active sites for grafting, hence grafting is possible.

As specific examples of the vinyl type polymerizable group-containingsilane or the silane having the group capable of radical reaction, theremay be mentioned, among others, (meth)acryloyloxy group-containingsilanes such as γ-methacryloyloxypropyldimethoxymethylsilane,γ-methacryloyloxypropyltrimethoxysilane,γ-methacryloyloxypropyltriethoxysilane,γ-methacryloyloxypropyldiethoxymethylsilane,γ-acryloyloxypropyldimethoxymethylsilane andγ-acryloyloxypropyltrimethoxysilane, vinylphenyl group-containingsilanes such as p-vinylphenyldimethoxymethylsilane andp-vinylphenyltrimethoxysilane, vinyl group-containing silanes such asvinylmethyldimethoxysilane, vinyltrimethoxysilane andvinyltriethoxysilane, and mercapto group-containing silanes such asmercaptopropyltrimethoxysilane and mercaptopropyldimethoxymethylsilane.Among these, (meth)acryloyloxy group-containing silanes, vinylgroup-containing silanes and mercapto group-containing silanes arepreferably used because of economical advantage. The vinyl typepolymerizable group-containing silanes or silanes having the groupcapable of radical reaction may be used singly or two or more of themmay be used in combination.

When the vinyl type polymerizable group-containing silane is of thetrialkoxysilane type, it also serves as such a tri- or furtherpoly-functional silane as mentioned below.

The tri- or further poly-functional silane mentioned above is used as acomponent to be copolymerized with the above-mentioned organosiloxane,bifunctional silane, vinyl type polymerizable group-containing silaneand/or silane having the group capable of radical reaction, amongothers, for the introduction of crosslinked structures into thepolyorganosiloxane to confer thereon elasticity as rubber, namely as acrosslinking agent for the polyorganosiloxane. Alternatively, it is usedas a component for increasing the molecular weight of thepolyorganosiloxane. As specific examples, there may be mentionedtetraethoxysilane, methyltriethoxysilane, methyltrimethoxysilane,ethyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane,heptadecafluorodecyltrimethoxysilane, trifluoropropyltrimethoxysilane,octadecyltrimethoxysilane, and like tetrafunctional and trifunctionalalkoxy silanes. Among these, tetraethoxysilane and methyltriethoxysilaneare preferably used because of high crosslinking efficiency.

The organosiloxane, bifunctional silane, vinyl type polymerizablegroup-containing silane, silane having the group capable of radicalreaction and tri- or further poly-functional silane are subjected topolymerization generally in such amounts that the organosiloxane and/orbifunctional silane (the ratio, by weight, between the organosiloxaneand bifunctional silane generally being 100/0 to 0/100, preferably 100/0to 70/30) amounts to 50 to 99.9%, preferably 60 to 99.5%, the vinyl typepolymerizable group-containing silane or silane having the group capableof radical reaction to 0 to 40%, preferably 0.5 to 30%, and the tri- orfurther poly-functional silane to 0 to 50%, preferably 0 to 39%. Eitherof the vinyl type polymerizable group-containing silane or silane havingthe group capable of radical reaction, and the tri- or furtherpoly-functional silane do not amount to 0% at the same time but any ofthem is preferably used in an amount of not less than 0.1%.

When the proportions of the organosiloxane and bifunctional silane areexcessively small, the resulting resin composition tends to becomebrittle. When they are too large, the flame retardancy and impactresistance may hardly be manifested and the final moldings tend to havea defective appearance. When the proportions of either of the vinyl typepolymerizable group-containing silane or the silane having the groupcapable of radical reaction, and the tri- or further poly-functionalsilane are excessively small, the flame retardancy and impact resistancemanifesting effects may be insignificant and/or the resulting moldingsmay have a defective appearance and, when they are excessive, theresulting resin composition tends to become brittle.

The tri- or further poly-functional silane mentioned above increases thetoluene insoluble matter content mentioned above in many instances and,therefore, it is desirable, from the viewpoint of the flame retardancyand impact resistance, not to use such a tri- or further poly-functionalsilane but to use the above-mentioned vinyl type polymerizablegroup-containing silane or silane having the group capable of radicalreaction alone together with the above-mentioned organosiloxane and/orbifunctional silane.

The polyorganosiloxane particles (B-1) mentioned above are preferablyproduced, for example, by emulsion-polymerizing apolyorganosiloxane-forming composition comprising the above-mentionedorganosiloxane, bifunctional silane, and vinyl type polymerizablegroup-containing silane or silane having the group capable of radicalreaction, optionally together with the tri- or further poly-functionalsilane, among others.

The emulsion-polymerization can be carried out, for example, byemulsifying and dispersing the polyorganosiloxane-forming composition inwater by mechanical shearing in the presence of an emulsifier andplacing the composition in an acidic condition. When, in that case,emulsion droplets not smaller than several micrometers in size areprepared by mechanical shearing, the volume average particle diameter ofthe polyorganosiloxane particles (B-1) obtained after polymerization canbe controlled within the range of 0.02 to 0.6 μm by selecting the amountof the emulsifier employed, the diameter of the emulsion dropletsmentioned above, and the inorganic or organic acid, which is to bementioned later herein, and the amount thereof, among others.

To produce the polyorganosiloxane particles with a narrow particlediameter distribution, the method which comprises using, as seedparticles, a vinyl (co)polymer prepared by (co)polymerizing the samevinyl monomer (e.g. styrene, butyl acrylate, methyl methacrylate) asused in the step of graft polymerization, which is to be mentioned laterherein, in the conventional manner of emulsion polymerization, andsubjecting an emulsion comprising emulsion droplets not smaller thanseveral micrometers in size as obtained, for example, by emulsificationby mechanical shearing of the above-mentioned polyorganosiloxane-formingcomposition, water and an emulsifier to emulsion polymerization in thepresence of the seed particles in an acidic condition may be used. Thevolume average particle diameter of the thus-obtainablepolyorganosiloxane particles can be controlled within the range of 0.01to 0.5 μm, and the variation coefficient in particle diameterdistribution within the range of 10 to 60%, in the same manner asmentioned above.

The above-mentioned emulsion droplets not smaller than severalmicrometers in size can be prepared by using a high-speed stirrer, suchas a homomixer.

The emulsion polymerization of the polyorganosiloxane-formingcomposition may be carried out in one stage or stepwise in two or morestages.

In the above emulsion polymerization, an emulsifier capable of retainingits emulsifying ability in an acidic condition is used. Specificexamples are alkylbenzenesulfonic acids, sodium alkylbenzenesulfonates,alkylsulfonic acids, sodium alkylsulfonates, sodium(di)alkylsulfosuccinates, sodium polyoxyethylene nonylphenyl ether-sulfonates,sodium alkyl sulfates, and the like. The emulsifiers may be used singlyor two or more of them may be used in combination. Among these,alkylbenzenesulfonic acids, sodium alkylbenzenesulfonates, alkylsulfonicacids, sodium alkylsulfonates, and sodium(di)alkyl sulfosuccinates arepreferred because of the relatively high emulsion stability they canprovide. Further, alkylbenzenesulfonic acids and alkylsulfonic acids areparticularly preferred since they can also serve as polymerizationcatalysts for the polyorganosiloxane-forming composition.

The acidic condition can be attained by addition of an inorganic acid,such as sulfuric acid or hydrochloric acid, or an organic acid, such asan alkylbenzenesulfonic acid, an alkylsulfonic acid or trifluoroaceticacid, to the system, and the pH is preferably adjusted to 1 to 3, morepreferably to 1.0 to 2.5, so that the production facilities may not becorroded and an appropriate rate of polymerization may be obtained.

The heating for polymerization is carried out preferably to 60 to 120°C., more preferably 70 to 100° C., so that an adequate rate ofpolymerization may be attained.

In an acidic condition, the Si—O—Si bonds forming the polyorganosiloxanemain chain are in equilibrium between cleavage and formation and thisequilibrium is temperature-dependent, hence it is preffered toneutralize with an aqueous solution of an alkali, such as sodiumhydroxide, potassium hydroxide or sodium carbonate, to stabilize thepolyorganosiloxane chain. Furthermore, as the temperature lowers, thatequilibrium shifts to siloxane bond formation side, favoring theformation of molecules higher in molecular weight or degree ofcrosslinking. Therefore, for attaining a high molecular weight or a highdegree of crosslinking, it is preferable that the polymerization of thepolyorganosiloxane-forming composition be carried out at 60° C. orhigher and the reaction mixture be then cooled to room temperature orbelow and, after about 5 to 100 hours of standing, neutralized.

The thus-obtained polyorganosiloxane particles (B-1), when formed bypolymerization, for example, of an organosiloxane or bifunctionalsilane, further with a vinyl type polymerizable group-containing silaneor silane having the group capable of radical reaction added thereto,generally occur as a polymer having vinyl type polymerizable groups orgroups capable of radical reaction resulting from randomcopolymerization. In cases where a tri- or further poly-functionalsilane is used for copolymerization, they occur as a crosslinked polymerhaving a network structure. When crosslinking between vinyl typepolymerizable groups is caused to occur with a radical polymerizationinitiator such as the one to be used in graft polymerization, which isto be mentioned later herein, they have a crosslinked structureresulting from chemical bonding between vinyl type polymerizable groups,with a part of the vinyl type polymerizable groups remaining unreacted.

The polyorganosiloxane-containing graft copolymer (B) is obtained bygraft-polymerizing, in at least one stage, a monomer (B-3) comprising apolyfunctional monomer (B-2) containing at least two polymerizableunsaturated bonds within the molecule, and/or a vinyl monomer (B-4) inthe presence of the polyorganosiloxane particles (B-1) obtained in theprocess mentioned above. In the above-mentioned graft polymerization,the so-called free polymer, namely a polymer resulting frompolymerization of the graft component to form the graft copolymer (here,a (co)polymer of the monomer (B-3) comprising the polyfunctional monomer(B-2), and/or the vinyl monomer (B-4)), without grafting onto the stemcomponent (here, the polyorganosiloxane particles (B-1)), giving amixture of the graft copolymer and free polymer. In the presentspecification, both of the polymers are collectively referred to as“graft copolymer”.

The polyfunctional monomer (B-2) containing at least two polymerizableunsaturated bonds within the molecule, which is to be used for theproduction of such graft copolymer (B), is a component serving toprevent the acetone insoluble matter content of the graft copolymer (B)from decreasing and improve the flame retardancy. The polyfunctionalmonomer (B-2) may also be used in the form of the monomer (B-3) inadmixture with another copolymerizable monomer (B-5). In that case, theproportion of the polyfunctional monomer (B-2) in the monomer (B-3) ispreferably 100 to 20% by weight, more preferably 100 to 50% by weight(correspondingly, the proportion of the copolymerizable monomer (B-5) inthe monomer (B-3) being preferably 0 to 80% by weight, more preferably 0to 50% by weight). When the proportion of the polyfunctional monomer(B-2) in the monomer (B-3) is too small, no satisfactory flameretardancy will be obtained.

As specific examples of the polyfunctional monomer (B-2), there may bementioned allyl methacrylate, allyl acrylate, triallyl cyanurate,triallyl isocyanurate, diallyl phthalate, ethylene glycoldimethacrylate, 1,3-butylene glycol dimethacrylate, and divinylbenzene,among others. The polyfunctional monomer (B-2) may comprise one singlespecies or a combination of two or more species. Among these, allymethacrylate, in particular, is preferably used due to the advantages ineconomy and effect. As examples of the other copolymerizable monomer(B-5), there may be mentioned the same species as those which are to begiven below as examples of the vinyl monomer (B-4). The copolymerizablemonomer (B-5) may comprise one single species or two or more species.

The vinyl monomer (B-4) used in the production of the graft copolymer(B) is a component leading good dispersion of the graft copolymer (B) inthe thermoplastic resin (A), which is to be described in detail laterherein, in the step of kneading therewith and thereby cause impactresistance manifestation.

As the vinyl monomer (B-4), there may be mentioned, for example,aromatic vinyl monomers such as styrene, α-methylstyrene,p-methylstyrene and p-butylstyrene, cyanovinyl monomers such asacrylonitrile and methacrylonitrile, (meth)acrylic ester monomers suchas methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate,2-ethylhexyl acrylate, glycidyl acrylate, hydroxyethyl acrylate,hydroxybutyl acrylate, methyl methacrylate, ethyl methacrylate, butylmethacrylate, lauryl methacrylate, glycidyl methacrylate andhydroxyethyl methacrylate, and carboxyl group-containing vinyl monomerssuch as itaconic acid, (meth)acrylic acid, fumaric acid and maleic acid.The vinyl monomer (B-4) may comprise one single species or a combinationof two or more species. A mixture of an aromatic vinyl monomer such asstyrene and a cyanovinyl monomer such as acrylonitrile, methylmethacrylate, and a mixture of methyl methacrylate as the main componentwith methyl acrylate, acrylonitrile or the like are preferred amongothers since they can lead to impact resistance manifestation in smallamounts.

The vinyl monomer (B-4) is one such that the polymer derived from thevinyl monomer (B-4) alone preferably has a solubility parameter of notless than 9.15 (cal/cm³)^(1/2), more preferably not less than 9.17(cal/cm³)^(1/2), still more preferably not less than 9.20(cal/cm³)^(1/2), but not more than 10.15 (cal/cm³)^(1/2), morepreferably not more than 10.10 (cal/cm³)^(1/2), still more preferablynot more than 10.05 (cal/cm³)^(1/2). When the solubility parameter isoutside the above range, both of the flame retardancy and impactresistance tend to deteriorate.

The solubility parameter is a value calculated by the group contributionmethod described in “Polymer Handbook”, published in 1999 by John Wiley& Sons, Ltd., 4th edition, Section VII, pages 682–685, using Small'sgroup parameters. For example, the value for poly(methyl methacrylate)(assumed repeating unit molecular weight 100 g/mol, assumed density 1.19g/cm³) is 9.25 [(cal/cm³)^(1/2)], for poly(butyl methacrylate) (assumedrepeating unit molecular weight 142 g/mol, assumed density 1.06 g/cm³)9.47 [(cal/cm³)^(1/2)], for poly(methyl acrylate) (assumed repeatingunit molecular weight 86 g/mol, assumed density 1.19 g/cm³) 9.47[(cal/cm³)^(1/2)], for poly(butyl acrylate) (assumed repeating unitmolecular weight 128 g/mol, assumed density 1.06 g/cm³) 8.97[(cal/cm³)^(1/2)], for polystyrene (assumed repeating unit molecularweight 104, assumed density 1.05 g/cm³) 9.03 [(cal/cm³)^(1/2)], and forpolyacrylonitrile (assumed repeating unit molecular weight 53, assumeddensity 1.18 g/cm³) 12.71 [(cal/cm³)^(1/2)]. The density values of thepolymers as used are the values described in Ullmann's Encyclopedia ofIndustrial Chemistry, published in 1992 by the publisher VCH, Vol. A21,page 169. As for the solubility parameter δc of a copolymer, the valuefor the main component is used when the weight fraction (of minorcomponent) is less than 5% and, when that weight fraction is not lessthan 5%, it is supposed that weight fraction-based additivity holdsgood. Thus, the solubility parameter of a copolymer constituted of mvinyl monomer species can be calculated from the solubility parameter δnof the homopolymer of each individual constituent vinyl monomer and theweight fraction Wn thereof according to the equation (1):

$\begin{matrix}{\delta_{c} = {\sum\limits_{n = 1}^{m}\;{\delta_{n}W_{n}}}} & (1)\end{matrix}$

Thus, as for the solubility parameter of a copolymer composed of 75% ofstyrene and 25% of acrylonitrile, for instance, a value of 9.95[(cal/cm³)^(1/2)] is obtained by making a calculation according to theequation (1) using the solubility parameter values 9.03[(cal/cm³)^(1/2)] for polystyrene and 12.71 [(cal/cm³)^(1/2)] forpolyacrylonitrile.

When different vinyl monomers or different vinyl monomer compositionsare polymerized in two or more stages, the solubility parameter δs ofthe vinyl polymer components in the graft copolymer obtained iscalculated supposing that additivity holds good using the weightfractions, namely the values obtained by dividing the weight of thevinyl polymer components obtained in the respective stages by the totalweight of the finally obtained vinyl polymer components. Thus, when thepolymerization is carried out in q stages, δs can be calculated from thesolubility parameter δi of the polymer obtained in the stage i and thecorresponding weight fraction Wi in accordance with the equation (2):

$\begin{matrix}{\delta_{s} = {\sum\limits_{i = 1}^{q}\;{\delta_{i}W_{i}}}} & (2)\end{matrix}$

For example, when the polymerization is carried out in two stages and 50parts by weight of a copolymer composed of 75% of styrene and 25% ofacrylonitrile is obtained in the first stage and 50 parts by weight of amethyl methacrylate polymer is obtained in the second stage, thesolubility parameter of the polymer obtained in this two-stagepolymerization is calculated according to the equation (2) using thesolubility parameter values 9.95 [(cal/cm³)^(1/2)] for the copolymer of75% styrene and 25% acrylonitrile and 9.25 [(cal/cm³)^(1/2)] forpoly(methyl methacrylate). A value of 9.60 [(cal/cm³)^(1/2)] is thusobtained.

In such graft copolymer (B), the polyorganosiloxane particles (B-1)preferably accounts for not less than 40 parts by weight (morepreferably not less than 63 parts by weight) but not more than 95 partsby weight (more preferably not more than 85 parts by weight), themonomer (B-3) comprising the polyfunctional monomer (B-2) and anothercopolymerizable monomer (B-5) preferably accounts for 0 to 10 parts byweight (more preferably 0 to 7 parts by weight), and the vinyl monomer(B-4) preferably accounts for not less than 5 parts by weight (morepreferably not less than 7 parts by weight) but not more than 50 partsby weight (more preferably not more than 30 parts by weight), per 100parts by weight of the whole graft copolymer. When the proportion of thepolyorganosiloxane particles (B-1) is higher (accordingly, that of thevinyl monomer (B-4) is lower), the graft copolymer (B) will not besatisfactorily dispersed in the thermoplastic resin (A), often leadingto decreases in impact resistance. Conversely, when that proportion istoo small (accordingly, that of the monomer (B-3) and/or vinyl monomer(B-4) is excessive), the flame retandancy tends to deteriorate. When theproportion of the monomer (B-3) is excessive, the impact resistance ofthe moldings finally obtained tends to decrease.

The graft copolymer (B) preferably has an acetone insoluble mattercontent (the weight percent of the acetone insoluble matter after 48hours of immersion of 1 g of the graft copolymer in 80 ml of acetone atroom temperature) of not lower than 80% by weight, more preferably notlower than 85% by weight, still more preferably not lower than 90% byweight, since good flame retardancy is achieved in such cases. Forobtaining such graft copolymer (B), it is necessary to select anappropriate vinyl type polymerizable group-containing silane or silanehaving the group capable of radical reaction, or use a sufficient amountof the polyfunctional monomer (B-2).

The vinyl type polymerizable group-containing silane can beappropriately selected, for example, from among (meth)acryloyloxygroup-containing silanes such asγ-methacryloyloxypropyldimethoxymethylsilane,γ-methacryloyloxypropyltrimethoxysilane,γ-methacryloyloxypropyltriethoxysilane,γ-methacryloyloxypropyldiethoxymethylsilane,γ-acryloyloxypropyldimethoxymethylsilane andγ-acryloyloxypropyltrimethoxysilane. In this case, the graft copolymer(B) can have an acetone insoluble matter content of not less than 80%,without using the polyfunctional monomer (B-2).

When a vinylphenyl group-containing silane such asp-vinylphenyldimethoxymethylsilane or p-vinylphenyltrimethoxysilane, avinyl group-containing silane such as vinylmethyldimethoxysilane,vinyltrimethoxysilane or vinyltriethoxysilane, or a mercaptogroup-containing silane such as mercaptopropyltrimethoxysilane ormercaptopropyldimethoxymethylsilane is selected as the vinyl typepolymerizable group-containing silane or silane having the group capableof radical reaction, the monomer (B-3) comprising the polyfunctionalmonomer (B-2) and another copolymerizable monomer (B-5) is preferablyused in an amount of 1.5 to 8 parts by weight, more preferably 2.5 to 7parts by weight, per 100 parts by weight of the whole graft copolymer(B). When the amount of the monomer (B-3) is too small, the acetoneinsoluble matter content will become lower than 80% and the flameretardancy will deteriorate. When the monomer (B-3) is excessive, theimpact resistance of the moldings finally obtained may become decreasedin some instances.

In obtaining the graft copolymer (B) according to the invention, theconventional seed emulsion polymerization technique can be applied. As asimple and convenient method, there may be mentioned the method whichcomprises radical (graft) polymerizing, in at least one stage, themonomer (B-3) and/or vinyl monomer (B-4) in the presence of thepolyorganosiloxane particles (B-1) occurring in a latex form. Thisradical polymerization may be carried out without any particularrestriction, for example by the method comprising thermally decomposinga radical polymerization initiator or by the method in a redox systemusing a reducing agent.

As specific examples of the radical polymerization initiator, there maybe mentioned organic peroxides such as cumene hydroperoxide, tert-butylhydroperoxide, benzoyl peroxide, tert-butyl peroxyisopropyl carbonate,di-tert-butyl peroxide, tert-butyl peroxylaurate, lauroyl peroxide,succinic acid peroxide, cyclohexanone peroxide and acetylacetoneperoxide, inorganic peroxides such as potassium persulfate and ammoniumpersulfate, and azo compounds such as 2,2′-azobisisobutyronitrile. Amongthese, organic peroxides and inorganic peroxides are particularlypreferred because easy to handle them in emulsion polymerization.

As the reducing agent used in the redox system, there may be mentionedsuch mixtures as ferrous sulfate/glucose/sodium pyrophosphate, ferroussulfate/dextrose/sodium pyrophosphate, and ferrous sulfate/sodiumformaldehyde sulfoxylate/salt of ethylenediamineacetic acid.

The radical polymerization initiator is used generally in an amount of0.005 to 20 parts by weight, preferably 0.01 to 10 parts by weight, mostpreferably 0.04 to 5 parts by weight, per 100 parts by weight of the sumof the monomer (B-3) and/or vinyl monomer (B-4) employed, or per 100parts by weight of the monomer(s) used in each stage in the case ofmultistage polymerization. When the polymerization is carried out in aplurality of stages, the radical polymerization initiators and theamounts thereof in the respective stages may be the same or different.When the amount of the radical polymerization initiator is smaller, therate of reaction will be low, resulting in a tendency toward poorproductivity. When it is excessive, the heat generated during reactiontends to become much, making it difficult to control the productionprocess.

Where necessary, a chain transfer agent may be used on the occasion ofradical polymerization. The chain transfer agent is not particularlyrestricted but may be any of those conventionally used in emulsionpolymerization. As examples, there may be mentionedtert-dodecylmercaptan, n-octylmercaptan, n-tetradecylmercaptan,n-hexylmercaptan and the like.

While it is an optional component, the chain transfer agent, when used,is used preferably in an amount of 0.01 to 5 parts by weight per 100parts by weight of the sum of the monomer (B-3) and/or vinyl monomer(B-4) employed, or per 100 parts by weight of the monomer(s) used ineach stage in the case of multistage polymerization. When thepolymerization is carried out in a plurality of stages, the chaintransfer agents and the amounts thereof in the respective stages may bethe same or different. When the amount of the chain transfer agent isless than 0.01 part by weight, the effect of the use thereof will not beobtained. When it exceeds 5 parts by weight, the rate of reaction tendsto become slow, resulting in reduced productivity.

Generally, the reaction temperature during polymerization is preferably30 to 120° C. for the ease of control.

In the above polymerization, when the polyorganosiloxane particles (B-1)are vinyl type polymerizable group- or ones having the group capable ofradical reaction, they serve as grafting reaction sites, and grafts areformed on the occasion of radical polymerization of the monomer (B-3)and/or vinyl monomer (B-4). When there are no vinyl type polymerizablegroups or groups capable of radical reaction on the polyorganosiloxaneparticles (B-1), the use of a specific radical initiator, for exampletert-butyl peroxylaurate, results in hydrogen abstraction from anorganic group (e.g. methyl group) bound to the silicon atom, and thethus-formed radicals induce polymerization of the monomer (B-3) and/orvinyl monomer (B-4) to form grafts. In cases where the monomer (B-3) issubjected to graft polymerization and then, further, the vinyl monomer(B-4) is subjected to graft polymerization, the vinyl monomer (B-4),when polymerized by means of a radical polymerization initiator, reactsnot only with the polyorganosiloxane particles (B-1), like the monomer(B-3), but also with unsaturated bonds in the polymer formed by thepolyfunctional monomer (B-2) in the monomer (B-3) to give grafts made ofthe vinyl monomer (B-4).

When the graft copolymer (B) occurs in a latex form, the particlediameter thereof is preferably not smaller than 0.01 μm, more preferablynot smaller than 0.03 μm, still more preferably not smaller than 0.10μm, but preferably not larger than 0.7 μm, more preferably not largerthan 0.5 μm, still more preferably not larger than 0.35 μm. Excessivelysmall or large particle diameters tend to cause decreases in impactresistance.

When the graft copolymer (B) is in a latex form, the variationcoefficient in particle diameter distribution is preferably not higherthan 100%, more preferably not higher than 60%, still more preferablynot higher than 40%. When the variation coefficient is excessively high,the flame retardancy may deteriorate in some instances. The lower limitto the coefficient of variation is not restricted, and a smaller valueis more preferred. It is difficult, however, to attain a value of nothigher than 5%.

The graft copolymer (B) obtained by emulsion polymerization can berecovered in the conventional manner, for example by the method(coagulation method) comprising adding an inorganic bivalent or furtherpolyvalent metal salt, such as calcium chloride, magnesium chloride,magnesium sulfate or aluminum chloride, to the latex to causecoagulation of the latex, and separating, washing with water,dehydrating and drying the coagulum. The method of coagulation is notparticularly restricted but various coagulation methods can be employed.Preferred from the viewpoint of flame retardancy, impact resistance andanti-blocking property, however, is the above-mentioned method of addingan inorganic bivalent or further polyvalent metal salt. Preferred, inparticular, as the inorganic bivalent or further polyvalent metal saltare inorganic alkaline earth metal salts, typically calcium chloride,magnesium chloride and magnesium sulfate, because of their beingavailable economically at low prices and, further, in view of the factthat they are safe in handling and rather friendly to the environment.By application of such inorganic bivalent or further polyvalent metalsalt, the emulsifier used in the step of emulsion polymerization isalmost quantitatively converted to the corresponding bivalent or furtherpolyvalent metal salt thereof, and the metal salt is contained in thegraft copolymer (B). The emulsifier-derived bivalent or furtherpolyvalent metal salt thus formed is effective as an ingredient capableof improving the powder characteristics, in particular the anti-blockingproperty, of the graft copolymer (B) according to the invention.

In the practice of the invention, the spray drying method can be used aswell. The recovery of the graft copolymer (B) as powder by the spraydrying method may be carried out while adding a bivalent or furtherpolyvalent metal salt of a sulfur-containing organic compound. As forthe method of addition, the above-mentioned bivalent or furtherpolyvalent metal salt may be added either in the form of a powder as itis or in the form of an aqueous dispersion. In the case of addition inthe form of an aqueous dispersion, drying is further continued to removemoisture finally to a substantial extent. The term “substantial extent”as used herein means that the weight fraction of the moisture containedin the mixture of the graft copolymer (B) recovered and the metal saltof the sulfur-containing organic compound is not more than 5% by weight,preferably not more than 2% by weight. Preferably, the bivalent orfurther polyvalent metal salt of the sulfur-containing organic compoundis not added to the latex but is added to sprayed particles duringdrying or to the powder obtained. When added to the latex, it may clog anozzle or cause the same kind of trouble, making spray drying impossiblein some cases.

When the bivalent or further polyvalent metal salt of thesulfur-containing organic compound is added in the form of a powder inthe step of spray drying, such fine mixing as realizable by thecoagulation method cannot be attained, hence the effect improvinganti-blocking property may be inferior as compared with the coagulationmethod in certain instances. Even when the bivalent or furtherpolyvalent metal salt of the sulfur-containing organic compound is addedin the form of an aqueous dispersion in the spray drying process, thebivalent or further polyvalent metal salt of the sulfur-containingorganic compound is added in the form of a slurry in some instancessince it is low in solubility in water and, on such occasions, theeffect improving anti-blocking property may sometimes be poor ascompared with the coagulation method.

The metal salt (C) to be used according to the invention may be at leastone species selected from the group consisting of alkali metal salts andbivalent or further polyvalent metal salts. From the viewpoint of flameretardancy, impact resistance and, further, anti-blocking property,alkali metal salts of sulfur-containing organic compounds and/orbivalent or further polyvalent metal salts of sulfur-containing organiccompounds are preferred. In a particularly preferred mode of theflame-retardant thermoplastic resin composition of the invention, thecomposition contains both an alkali metal salt of a sulfur-containingorganic compound and a bivalent or further polyvalent metal salt of asulfur-containing organic compound.

When used in combination with the polyorganosiloxane-containing graftcopolymer (B), the alkali metal salt of the sulfur-containing organiccompound, which can be used in the practice of the invention, cansynergistically enhance the flame retardancy. The above-mentioned alkalimetal salt may comprise one single species or a combination of two ormore species.

The sulfur-containing organic compound mentioned above is preferably asulfonic acid, a sulfonamide, or a sulfuric ester. More preferably, asulfonic acid is selected, among others, from the viewpoint of flameretardancy and, most preferably, an (alkyl)aromatic sulfonic acid, aperfluoroalkanesulfonic acid, an aliphatic sulfonic acid or a diphenylsulfone sulfonic acid is selected. The alkali metal salt-forming metalincludes sodium, potassium, lithium, rubidium, cesium, and so forth.Preferred are sodium and potassium.

Preferably selected as the (alkyl)aromatic sulfonic acid aredodecylbenzenesulfonic acid, p-toluenesulfonic acid,dichlorobenzenesulfonic acid, benzenesulfonic acid, naphthalenesulfonicacid, and the like. These are most preferably used in the potassium orsodium salt form, among others.

Preferably selected as the perfluoroalkanesulfonic acid are sulfonicacids having a perfluoroalkane group preferably containing 1 to 19carbon atoms, more preferably 4 to 8 carbon atoms, more preferablyperfluorobutanesulfonic acid, perfluoromethylbutanenesulfonic acid,perfluorooctanesulfonic acid, and the like. These are most preferablyused in the sodium or potassium salt form, among others.

Preferably selected as the aliphatic sulfonic acid are, for example,alkylsulfonic acids such as dodecylsulfonic acid, dialkylsulfosuccinates such as dioctyl sulfosuccinate and didodecylsulfosuccinate, and the like. These are preferably used in the potassiumor sodium salt form, among others.

Preferably selected as the diphenyl sulfone sulfonic acid are, forexample, diphenyl sulfone-3-sulfonic acid, 4,4′-dibromodiphenylsulfone-3-sulfonic acid, 4-chloro-4′-nitrodiphenyl sulfone-3-sulfonicacid, diphenyl sulfone-3,3′-disulfonic acid, and the like. These arepreferably used in the (di)sodium or (di)potassium salt form, amongothers.

Preferably selected as the sulfonamide are, for example, saccharin,N-(p-tolylsulfonyl)-p-toluenesulfimide,N-(N′-benzylaminocarbonyl)sulfanilimide,N-(phenylcarboxyl)sulfanilimide, and the like. These are preferably usedin the potassium or sodium salt form, among others.

Preferably selected as the sulfuric ester are alkyl sulfuric acidmonoesters, typically dodecyl sulfuric acid monoester, and the like.These are preferably used in the potassium or sodium salt form, amongothers.

Among those mentioned above, potassium salt of diphenylsulfone-3-sulfonic acid, potassium salt of perfluorobutanesulfonic acid,sodium salt of dodecylbenzenesulfonic acid, and potassium salt ofdodecylbenzenesulfonic acid are particularly preferably used since theyare quite chlorine-free and bromine-free and can manifest flameretardancy at low addition levels. Most preferred are (alkyl)aromaticsulfonic acids, typically dodecylbenzenesulfonic acid, in the sodiumsalt form because of their commercial availability at low prices.

The bivalent or further polyvalent metal salt of the sulfur-containingorganic compounds, which can be used in the practice of the invention,can improve the powder characteristics, in particular the anti-blockingproperty, of the graft copolymer (B) of the invention in the step ofrecovery thereof, without impairing the thermal stability of theresulting flame-retardant thermoplastic resin compositions. These may beused singly, or two or more of them may be used in combination. Thesulfur-containing organic compound to be used here may be the same as ordifferent from the above-mentioned sulfur-containing organic compoundused in the form of an alkali metal salt. The addition of metal salts ofother compounds than the sulfur-containing organic compounds causescoloration of the moldings or otherwise impair the thermal stability ofthe thermoplastic resin compositions obtained and, in certain instances,cause deterioration of the thermoplastic resins so as to make the stepof molding itself impossible, hence are not preferred. On the otherhand, with the sulfur-containing organic compound in a univalent metalsalt form alone, it is difficult to give the effect improvinganti-blocking property to a satisfactory extent. Preferably, asulfur-containing organic compound is selected from among such ones asmentioned hereinabove referring to the alkali metal salt of thesulfur-containing organic compound and is used in the form of analkaline earth metal salt, for example calcium salt or magnesium salt.

The metal salt (C) is used in an amount of not less than 0.0005 part byweight (preferably not less than 0.001 part by weight, more preferablynot less than 0.004 part by weight) but not more than 5 parts by weight(preferably not more than 0.8 part by weight, still more preferably notmore than 0.2 part by weight), per 100 parts by weight of thethermoplastic resin (A). When the level of addition of the metal salt(C) is lower, no effect will be produced and, when it is excessive,molding faults, such as tanning of resin, may occur in the step ofmolding.

The flame-retardant thermoplastic resin composition of the invention,when it further contains an antioxidant (E), can show enhanced flameretardancy . The level of addition is preferably not more than 2 partsby weight, more preferably not more than 0.8 part by weight, still morepreferably not more than 0.7 part by weight, per 100 parts by weight ofthe thermoplastic resin (A). At levels exceeding 2 parts by weight, theimpact resistance tends to decrease. The lower limit is preferably 0.05part by weight. Although the mechanisms by the antioxidant are not knownin the case of the invention, the antioxidant is supposed to contributeto the prevention of degradation of the thermoplastic resin or of thegraft component of the polyorganosiloxane-containing graft copolymer (B)on molding. The antioxidant (E) may comprise one single species or acombination of two or more species.

The combined use, as the antioxidant (E), of at least one antioxidanthaving the isocyanuric ring structure within the molecule and at leastone other antioxidant is particularly effective. The proportion of theat least one antioxidant having the isocyanuric ring structure withinthe molecule in the total antioxidant is preferably not less than 10% byweight, more preferably not less than 20% by weight, but preferably notmore than 90% by weight, still more preferably not more than 80% byweight. In higher or lower proportions, the effect improving flameretardancy will be barely obtained and, in some instances, a detrimentaleffect may be produced. The antioxidant having the isocyanuric ringstructure within the molecule is, for example,tris(3,5-di-tert-butyl-4-hydroxybenzyl) isocyanurate. As otherantioxidants, there may be mentioned, for example,1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, dilaurylthiodipropionate, distearyl thiodipropionate, dimyristylthiodipropionate, and like dialkyl thiodipropionates.

The thermoplastic resin (A) used in the practice of the invention is notparticularly restricted but, from the viewpoint of impact resistance, itpreferably comprises at least one thermoplastic resin selected form thegroup consisting of acrylonitrile-styrene copolymers,acrylonitrile-butadiene rubber-styrene copolymers (ABS resins),acrylonitrile-butadiene rubber-a-methylstyrene copolymers,styrene-butadiene rubber-acrylonitrile-N-phenylmaleimide copolymers,acrylonitrile-acrylic rubber-styrene copolymers (AAS resins),acrylonitrile-acrylic rubber-a-methylstyrene copolymers, styrene-acrylicrubber-acrylonitrile-N-phenylmaleimide copolymers,acrylonitrile-acrylic/silicone composite rubber-styrene copolymers,acrylonitrile-acrylic/silicone composite rubber-a-methylstyrenecopolymers, styrene-acrylic/silicone compositerubber-acrylonitrile-N-phenylmaleimide copolymers,acrylonitrile-ethylene/propylene rubber-styrene copolymers (AES resins),polycarbonates, polyesters, polyphenylene ether, polystyrene,poly(methyl methacrylate), methyl methacrylate-styrene copolymers andpolyamides, in particular.

In the practice of the invention, the thermoplastic resin (A) ispreferably a polycarbonate-based resin. The polycarbonate-based resinpreferably comprises not less than 70% by weight, more preferably notless than 85% by weight, of a polycarbonate resin. Most preferably, itsubstantially comprises a polycarbonate resin alone. By saying“substantially comprises a polycarbonate resin alone” herein, it ismeant that the polycarbonate resin accounts for at least 95% by weight.When the polycarbonate resin proportion is within the above range, bothgood flame retardancy and high impact resistance can be obtained at thesame time. Such effects become better as the polycarbonate resinproportion increases and, with substantially the polycarbonate resinalone, the effects become maximal. As the component other than thepolycarbonate resin in the polycarbonate-based resin, there may bementioned, among others, those thermoplastic resins mentioned above. Thepolycarbonate resin may comprise one single species or a combination oftwo or more species.

The polycarbonate resin is not particularly restricted but includesvarious species. Generally, aromatic polycarbonates produced by thereaction of a dihydric phenol and a carbonate precursor can be used.Thus, use can be made of those produced by reacting a dihydric phenolwith a carbonate precursor by the solution method or fusion method,namely by reacting the dihydric phenol with phosgene or by reacting thedihydric phenol with diphenyl carbonate in the manner oftransesterification.

The dihydric phenol includes various species, in particular2,2-bis(4-hydroxyphenyl)propane [bisphenol A],bis(4-hydroxyphenyl)methane, 1,1-bis(4-hydroxyphenyl)ethane,2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane, 4,4′-dihydroxydiphenyl,bis(4-hydroxyphenyl)cycloalkanes, bis(4-hydroxyphenyl) oxide,bis(4-hydroxyphenyl) sulfide, bis(4-hydroxyphenyl) sulfone,bis(4-hydroxyphenyl) sulfoxide, bis(4-hydroxyphenyl) ether,bis(4-hydroxyphenyl) ketone, and the like.

Most preferred dihydric phenols are bis(hydroxyphenyl)alkane type ones,in particular ones comprising bisphenol A as the main material. Thecarbonate precursor includes carbonyl halides, carbonyl esters, andhaloformates, among others, and, more specifically, there may bementioned phosgene, dihydric phenol dihaloformates, diphenyl carbonate,dimethyl carbonate, diethyl carbonate, and the like.

In addition, the dihydric phenol further includes hydroquinone,resorcinol, catechol and the like. The dihydric phenols may be usedsingly or two or more of them may be used in admixture.

The polycarbonate resin may have a branched structure, and the branchingagent includes 1,1,1-tris(4-hydroxyphenyl)ethane,α,α′,α″-tris(4-hydroxyphenyl)-1,3,5-triisopropylbenzene, phloroglucinol,trimellitic acid, isatinbis(o-cresol) and the like. Phenol,p-tert-butylphenol, p-tert-octylphenol, p-cumylphenol or the like isused for the adjustment of molecular weight.

Such copolymers as polyester-polycarbonate resins or mixtures of variouspolycarbonate-based resins may also be used as the polycarbonate-basedresin. When such a copolymer as mentioned above is used, an adjustmentis made for the carbonate unit proportion in the polymer to fall withinthe range mentioned above.

The lower limit to the viscosity average molecular weight of thepolycarbonate-based resin is preferably not lower than 13,000, morepreferably not lower than 15,000. The upper limit is preferably nothigher than 25,000, more preferably not higher than 22,000, still morepreferably not higher than 20,000. When the viscosity average molecularweight is too low, the impact resistance tends to decrease and, when theviscosity average molecular weight is excessively high, the moldabilitytends to become worse. The viscosity average molecular weight (Mv) isthe value determining by measuring the viscosity of a methylene chloridesolution at 20° C. using an Ubbelohde's viscometer, determining thelimiting viscosity [η], and making a calculation according to theequation: [η]=1.23×10⁻⁵ Mv^(0.83). Two or more polycarbonate resinsdiffering in molecular weight may be used as a blend.

In the flame-retardant thermoplastic resin composition of the invention,there may be further incorporated a fluororesin (D). The fluororesinprevents the resin melted in combustion testing, such as the testaccording to UL-94, from falling dropwise (or dripping). As specificexamples which are preferred in view of their high dripping preventiveeffect, there may be mentioned polymonofluoroethylene,polydifluoroethylene, polytrifluoroethylene, polytetrafluoroethylene,tetrafluoroethylene/hexafluoroethylene copolymers and other fluorinatedpolyolefin resins as well as poly(vinylidene fluoride) resins. Thefluororesin (D) may comprise one single species or a combination of twoor more species.

The fluororesin (D) is used in an amount of not more than 2 parts byweight, preferably not more than 1 part by weight, more preferably notmore than 0.6 part by weight, per 100 parts by weight of thethermoplastic resin (A). While the dripping preventive effect increasesas the amount of the fluororesin increases, an excessively large amountthereof unfavorably results in a cost increase, with the drippingpreventive effect reaching a point of saturation. The fluororesin (D) isused in an amount of not less than 0.05 part by weight, preferably notless than 0.1 part by weight, more preferably not less than 0.2 part byweight.

In the flame-retardant thermoplastic resin composition of the invention,there may further be incorporated one or more of pigments, fillers,impact modifiers, antioxidants other than the antioxidant (E),ultraviolet absorbers, glass fibers, lubricants, polymeric lubricants,and so forth.

The flame-retardant thermoplastic resin composition of the invention canbe produced by blending the respective components/ingredients togetherand melt-kneading the mixture. When the polyorganosiloxane-containinggraft copolymer (B) contains metal salt (C), it is not necessary toseparately add a metal salt (C). However, a metal salt (C) may be addedseparately.

The flame-retardant thermoplastic resin composition of the invention,when it contains both an alkali metal salt of a sulfur-containingorganic compound and a bivalent or further polyvalent metal salt of asulfur-containing organic compound as the metal salt (C), is preferablyproduced by emulsion-polymerizing, in at least one stage, the monomer(B-3) comprising the polyfunctional monomer (B-2) containing at leasttwo polymerizable unsaturated bonds within the molecule, and/or thevinyl monomer (B-4) in the presence of the polyorganosiloxane particles(B-1), then recovering, by the coagulation method using an inorganicsalt of a bivalent or further polyvalent metal, the resultingpolyorganosiloxane-containing graft copolymer containing the bivalent orfurther polyvalent metal salt of the emulsifier-derivedsulfur-containing organic compound, and mixing up, by melt kneading, thethermoplastic resin (A), the polyorganosiloxane-containing graftcopolymer containing the bivalent or further polyvalent metal salt ofthe sulfur-containing organic compound, the alkali metal salt of thesulfur-containing organic compound, and the fluororesin (D) In the stepof melt kneading, a bivalent or further polyvalent metal salt of asulfur-containing organic compound may be added separately.

It is also possible to produce the composition of the invention by firstemulsion-polymerizing, in at least one stage, the monomer (B-3)comprising the polyfunctional monomer (B-2) containing at least twopolymerizable unsaturated bonds within the molecule, and/or the vinylmonomer (B-4) in the presence of the polyorganosiloxane particles (B-1),then recovering, by the spray drying method, the resultingpolyorganosiloxane-containing graft copolymer containing the alkalimetal salt of the emulsifier-derived sulfur-containing organic compound,and mixing up, by melt kneading, the thermoplastic resin (A), thepolyorganosiloxane-containing graft copolymer containing the alkalimetal salt of the sulfur-containing organic compound, the bivalent orfurther polyvalent metal salt of the sulfur-containing organic compound,and the fluororesin (D). In the step of melt kneading, an alkali metalsalt of a sulfur-containing organic compound may be added separately.

Further, it is possible to produce the composition of the invention byfirst emulsion-polymerizing, in at least one stage, the monomer (B-3)comprising the polyfunctional monomer (B-2) containing at least twopolymerizable unsaturated bonds within the molecule, and/or the vinylmonomer (B-4) in the presence of the polyorganosiloxane particles (B-1),then recovering, by the spray drying method with adding a bivalent orfurther polyvalent metal salt of a sulfur-containing organic compoundduring spray drying, the resulting polyorganosiloxane-containing graftcopolymer containing an alkali metal salt of the emulsifier-derivedsulfur-containing organic compound and the bivalent or furtherpolyvalent salt of the sulfur-containing organic compound, and mixingup, by melt kneading, the thermoplastic resin (A), thepolyorganosiloxane-containing graft copolymer containing the alkalimetal salt of the sulfur-containing organic compound and the bivalent orfurther polyvalent metal salt of the sulfur-containing organic compound,and the fluororesin (D) In the step of melt kneading, an alkali metalsalt of a sulfur-containing organic compound and/or a bivalent orfurther polyvalent metal salt of a sulfur-containing organic compoundmay be added separately.

The thus-obtained flame-retardant thermoplastic resin composition isexcellent in flame retardancy and impact resistance.

In the flame-retardant thermoplastic resin composition of the invention,there may be incorporated another flame retardant. As specific examplesof the flame retardant to be used in combination which are preferredbecause of their being halogen-free and phosphorus-free, for instance,there may be mentioned organic silicone compounds and/or silica, inparticular aromatic group-containing organic silicone compounds otherthan the polyorganosiloxane-containing graft copolymer. Further, theremay be mentioned triazine compounds such as cyanuric acid and melaminecyanurate, and boron compounds such as boron oxide and zinc borate,among others. It is also possible to combinedly use a phosphoruscompound such as triphenyl phosphate, condensed phosphoric acid ester,or stabilized red phosphorus. In this case, the employment of theflame-retardant thermoplastic resin composition of the invention inphosphorus-based flame retardant-containing compositions canadvantageously reduce the phosphorus-based flame retardant level inthose compositions.

The flame-retardant thermoplastic resin composition of the invention canbe molded by any of the molding methods used in molding thermoplasticresin compositions in general, namely by the injection molding,extrusion molding, blow molding, calender molding or like moldingmethod, for use in those fields in which flame retardancy and impactresistance are required, including, but not limited to, housings andchassis of various OA/information/household electric appliances such asdesktop computers, notebook computers, tower computers, printers,copiers, facsimile telegraphs, cellular phones, PHS phones, televisions,and video recorders, parts or members of various building materials, andvarious automotive parts or members, among others. The moldings obtainedare excellent in impact resistance and flame retardancy.

The flame retardant for thermoplastic resins as provided by the presentinvention comprises a polyorganosiloxane-containing graft copolymerobtained by polymerizing, in at least one stage, a monomer (B-3)comprising a polyfunctional monomer (B-2) containing at least twopolymerizable unsaturated bonds within the molecule, and/or a vinylmonomer (B-4) in the presence of polyorganosiloxane particles (B-1), analkali metal salt of a sulfur-containing organic compound, and abivalent or further polyvalent metal salt of a sulfur-containing organiccompound. The respective components are as described hereinabove. Theflame retardant for thermoplastic resins as provided by the presentinvention is excellent in powder properties, in particular anti-blockingproperty, and therefore is easy to handle and, when incorporated in suchthermoplastic resins as mentioned above, can give thermoplastic resincompositions excellent in flame retardancy and impact resistance.

The flame retardant for thermoplastic resins according to the inventioncan be produced by emulsion-polymerizing, in at least one stage, themonomer (B-3) comprising the polyfunctional monomer (B-2) containing atleast two polymerizable unsaturated bonds within the molecule, and/orthe vinyl monomer (B-4) in the presence of the polyorganosiloxaneparticles (B-1), then recovering, by the coagulation method using aninorganic salt of a bivalent or further polyvalent metal, the resultingpolyorganosiloxane-containing graft copolymer containing the bivalent orfurther polyvalent metal salt of the emulsifier-derivedsulfur-containing organic compound, and mixing up thepolyorganosiloxane-containing graft copolymer containing the bivalent orfurther polyvalent metal salt of the sulfur-containing organic compound,and the alkali metal salt of the sulfur-containing organic compound. Onthe occasion of melt kneading, a bivalent or further polyvalent metalsalt of a sulfur-containing organic compound may be added separately.

The flame retardant can also be produced by emulsion-polymerizing, in atleast one stage, the monomer (B-3) comprising the polyfunctional monomer(B-2) containing at least two polymerizable unsaturated bonds within themolecule, and/or the vinyl monomer (B-4) in the presence of thepolyorganosiloxane particles (B-1), then recovering, by the spray dryingmethod, the resulting polyorganosiloxane-containing graft copolymercontaining an alkali metal salt of the emulsifier-derivedsulfur-containing organic compound, and mixing up thepolyorganosiloxane-containing graft copolymer containing the alkalimetal salt of the sulfur-containing organic compound, and a bivalent orfurther polyvalent metal salt of a sulfur-containing organic compound.On the occasion of the above mixing, an alkali metal salt of asulfur-containing organic compound may be added separately.

Further, it is possible to produce the flame retardant byemulsion-polymerizing, in at least one stage, the monomer (B-3)comprising the polyfunctional monomer (B-2) containing at least twopolymerizable unsaturated bonds within the molecule, and/or the vinylmonomer (B-4) in the presence of the polyorganosiloxane particles (B-1),and then carrying out the spray drying method with adding a bivalent orfurther polyvalent metal salt of a sulfur-containing organic compoundduring spray drying.

BEST MODE FOR CARRYING OUT THE INVENTION

The following examples illustrate the present invention morespecifically. They are, however, by no means limitative of the scope ofthe invention. Hereinafter, “part(s)” means “part(s) by weight”.

The measurements and tests in the following Examples and ComparativeExamples were carried out in the following manner.

[Solid Matter Content]

Each latex was dried in a hot air drier at 120° C. for 2 hours, and thesolid matter content was calculated as (weight of the residue after 2hours of drying of the latex at 130° C.)/(latex weight before drying).

[Conversion of Monomers]

The conversion was calculated as (total charge (parts)×solid mattercontent−(emulsifier charged (parts)+inorganic acid and/or organic acidcharged (parts)+radical polymerization initiator charged(parts)/(monomer(s) charged (parts)).

[Toluene Insoluble Matter Content]

A 0.5-g portion of the polyorganosiloxane particles in solid form asobtained by drying each latex was immersed in 80 ml of toluene at roomtemperature for 24 hours, followed by 60 minutes of centrifugation at12,000 rpm. The toluene insoluble matter content of thepolyorganosiloxane particles was measured and expressed in terms ofweight percentage (%)

[Acetone Insoluble Matter Content]

One gram of each graft copolymer was immersed in 80 ml of acetone atroom temperature for 48 hours, followed by 10 minutes of centrifugationat 18,000 rpm. The sediment fraction was measured as the acetoneinsoluble matter content of the graft copolymer.

[Volume Average Particle Diameter]

The volume average particle diameter of the polyorganosiloxane particlesand of the graft copolymer was measured in a latex form. Using themeasurement apparatus MICROTRAC UPA (product of Leed & NorthrupInstruments), the volume average particle diameter (μm) and thevariation coefficient in particle diameter distribution (standarddeviation/volume average particle diameter (%)) were measured by thelight scattering method.

[Impact Resistance]

The evaluation was made by the Izod test at −10° C. using notched ⅛ inchbars according to ASTM D-256.

[Flame Retardancy]

The evaluation was made by the UL94 V test. In the evaluation,1.2-mm-thick specimens were also used in addition to 1.6-mm-thick ones.

[Anti-Blocking Property]

A 30-g portion of each graft copolymer composition in powder form wasplaced in a cylindrical vessel with a diameter of 50 mm, a load of 1kg/cm² was applied to the powder at 4° C. for 3 hours to give a block.Using Hosokawa Micron Corporation's powder tester PEE, vibrations of 60Hz were transmitted to the block for 100 seconds to disintegrate thesame. The proportion of the powder fraction passing through a 18-meshsieve to the total amount of the powder was determined. A highernumerical value indicates a higher level of anti-blocking property.

REFERENCE EXAMPLE 1 Production of Polyorganosiloxane Particles (S-1)

An emulsion was prepared by stirring an aqueous solution composed of thefollowing components at 8,000 rpm for 5 minutes using a homomixer.

Component Amount (parts) Pure water 250 Sodium dodecylbenzenesulfonate(SDBS) 1.0 Octamethylcyclotetrasiloxane (D4) 97γ-Methacryloyloxypropyldimethoxymethylsilane 3

This emulsion was charged, all at once, into a 5-nekced flask equippedwith a stirrer, reflux condenser, nitrogen inlet, monomer addition inletand thermometer. While stirring the system, 1 part (as solid) of a 10%aqueous solution of dodecylbenzenesulfonic acid (DBSA) was added, thetemperature was raised to 80° C. over about 40 minutes and, then, thereaction was allowed to proceed at 80° C. for 10 hours. Thereafter, thereaction mixture was cooled to 25° C. and, after 20 hours of standing,the pH of the system was readjusted to 6.5 with sodium hydroxide and thepolymerization was finished to give a latex containingpolyorganosiloxane particles (S-1). The conversion of monomers, and thevolume average particle diameter and toluene insoluble matter content ofthe polyorganosiloxane particle latex were measured. The results areshown in Table 1.

REFERENCE EXAMPLE 2 Production of Polyorganosiloxane Particles (S-2)

A 5-necked flask equipped with a stirrer, reflux condenser, nitrogeninlet, monomer addition inlet and thermometer was charged with:

Component Amount (parts) Pure water 186 SDBS 2

Then, the temperature was raised to 70° C. while purging the system withnitrogen, an aqueous solution composed of 4 parts of pure water and 0.1part of potassium persulfate (KPS) was then added, followed bycontinuous addition, over 1 hour, of a mixture composed of:

Component Amount (parts) Styrene (St) 0.5 Butyl acrylate (BA) 1.5Tert-Dodecylmercaptan (t-DM) 0.15.The mixture was stirred for 1 hour to complete the polymerization. ASt-BA copolymer latex was thus obtained. The conversion of monomers was99%. The latex obtained has a solid matter content of 2.0% and a volumeaverage particle diameter of 0.02 μm. At that time, the variationcoefficient was 39%. The St-BA copolymer had a toluene insoluble mattercontent of 0%.

Separately, a polyorganosiloxane-forming component emulsion was preparedby stirring a mixture composed of the following components at 8,000 rpmfor 5 minutes using a homomixer.

Component Amount (parts) Pure water 70 SDBS 0.5 D4 95Mercaptopropyldimethoxymethylsilane (MPDS) 5

Then, the St-BA copolymer-containing latex was maintained at 80° C., 1.2parts (as solid) of a 10% aqueous solution of DBSA was added and, then,the above polyorganosiloxane-forming component emulsion was added all atonce. After 15 hours of continued stirring, the reaction mixture wascooled to 25° C. and allowed to stand for 25 hours. The pH was thenadjusted to 6.4 with sodium hydroxide, and the polymerization wasfinished to give a latex containing polyorganosiloxane particles (S-2).The conversion of monomers, and the volume average particle diameter andtoluene insoluble matter content of the polyorganosiloxaneparticle-containing latex were measured. The results are shown inTable 1. The polyorganosiloxane particles were composed of 98% by weightof the polyorganosiloxane component and 2% by weight of the St-BAcopolymer component.

REFERENCE EXAMPLE 3 Production of Vinyl-Based Seed Particles (Sv-1)

The St-BA copolymer as produced in the course of production of thepolyorganosiloxane particles (S-2) in Reference Example 2 was used asvinyl-based seed particles (Sv-1). The vinyl-based seed particles (Sv-1)was measured for volume average particle diameter and toluene insolublematter content. The results are shown in Table 1.

TABLE 1 Reference Reference Reference Example 1 Example 2 Example 3Polyorganosiloxane particles S-1 S-2 Sv-1 or vinyl-based seed particlesConversion of monomers of 87 87 — polyorganosiloxane component (%)Average particle diameter 0.17 0.29 0.02 (μm) Variation coefficient (%)37 35 39 Toluene insoluble matter 0 0 0 content (%)

REFERENCE EXAMPLES 4 TO 12

A 5-necked flask equipped with a stirrer, reflux condenser, nitrogeninlet, monomer addition inlet and thermometer was charged with 300 partsof pure water (inclusive of that portion derived from thepolyorganosiloxane particle (B-1) latex), 0.4 part of sodiumformaldehyde sulfoxylate (SFS), 0.01 part of disodiumethylenediaminetetraacetate (EDTA), 0.0025 part ferrous sulfate and thepolyorganosiloxane particle (B-1) latex specified in Table 2. Under anitrogen sweep, the temperature was raised to 50° C. while stirring thesystem. After arrival at 50° C., a mixture of the monomer (B-3) andradical polymerization initiator specified in Table 2 was added over theperiod specified in Table 2 and, then, stirring was continued at 50° C.for 1 hour. Thereafter, a mixture of the monomer (B-4) and radicalpolymerization initiator specified in Table 2 was further added dropwiseover the period specified in Table 2. After completion of the adding themixture, stirring was continued for 4 hours to give a graft copolymerlatex. In Reference Examples 4 to 6, the addition of the monomer (B-3)mixture was omitted, and the monomer (B-4) mixture was added instead.

Then, the latex was diluted with pure water to a solid concentration of15%, 2.5 parts (as solid) of a 2% aqueous solution of calcium chloridewas added to give a coagulated slurry. The coagulated slurry was heatedto 98° C. with stirring, then cooled to 50° C., dehydrated and dried ina hot air drier at 50° C. for 72 hours to give apolyorganosiloxane-containing graft copolymer (SG-1 to SG-9) in powderform. The conversion of monomers and the acetone insoluble mattercontent of each polymer are shown in Table 2.

TABLE 2 Reference Example 4 5 6 7 8 9 10 11 12 Polyorganosiloxane S-1 8565 92 — — — — — — particles (B-1) or S-2 — — — 60 75 75 89 89 89vinyl-based seed Sv-1 — — — — — — — — — particles (parts) Vinyl monomerAIMA — — —   3.8   3.8   3.8   1.9   1.9   1.9 (B-3) (parts) BA — — —  0.2   0.2   0.2   0.1   0.1   0.1 CHP — — — — — — — —    0.05 TBP — —— — — — —    0.06 — TBPIPC — — —    0.12   0.12    0.11    0.06 — — Ad-— — — All at All at All at All at All at All at dition once once onceonce once once period (h) Vinyl monomer MMA 15 35  8 36 — 16 9 9 9 (B-4)(parts) MA — — — — —  5 — — — St — — — —   15.8 — — — — AN — — — —   5.3— — — — CHP    0.06    0.14    0.03 — — — — —    0.06 TBP — — — — — — —  0.1 — TBPIPC — — — 0.4   0.6   0.2   0.1 — — Ad-  2  4  1  4  2  2  1 1  1 dition period (h) SP of polymer (B-4)    9.25    9.25    9.25   9.25    9.95    9.30    9.25    9.25    9.25 ((cal/cm³)^(1/2))Conversion (%) (B-3) — — — 99 99 99 99 99 99 (B-4) 99 100  98 99 99 9999 98 100  Acetone insoluble matter 96 88 98 90 91 95 99 98 97 content(%) Graft polymer No. SG-1 SG-2 SG-3 SG-4 SG-5 SG-6 SG-7 SG-8 SG-9Reference Example 13 14 15 16 17 18 19 20 Polyorganosiloxane S-1 — — — —— — — — particles (B-1) or S-2 — — — — — — 89 89 vinyl-based seed Sv-1 2  5  5  5 — — — — particles (parts) Vinyl monomer AIMA   2.8 — —   0.9  5.7  1   1.9   1.9 (B-3) (parts) BA   0.2 — —   74.1   0.3 79   0.1  0.1 CHP — — — — — — — — TBP — — — — — — — — TBPIPC    0.09 — —   0.4   0.18   0.4    0.06    0.06 Addition All at — — 10 All at 10 All atAll at period (h) once (Dropwise once (Dropwise once once addition)addition) Vinyl monomer MMA 95 95 — 20 94 20  9  9 (B-4) (parts) MA — —— — — — — — St — —   71.3 — — — — — AN — —   23.8 — — — — — CHP — — — —— — — TBP — — — — — — — — TBPIPC   0.6   0.6   0.8   0.2   0.6   0.2  0.1   0.1 Addition 10 10 10  2 10  2  1  1 period (h) SP of polymer(B-4)    9.25    9.25    9.95    9.25    9.25    9.25    9.25    9.25((cal/cm³)^(1/2)) Conversion (%) (B-3) 99 — — 98 90 98 99 99 (B-4) 98 9794 100  98 99 99 99 Acetone insoluble 12  8 10 91 15 92 98 98 mattercontent (%) Graft polymer No. SG′-1 SG′-2 SG′-3 SG′-4 SG′-5 SG′-6 SG′-7SG-10

In the table, AlMA stands for allyl methacrylate, BA for butyl acrylate,MA for methyl acrylate, MMA for methyl methacrylate, St for styrene, ANfor acrylonitrile (all being monomers), CHP for cumene hydroperoxide,TBP for tert-butyl hydroperoxide, TBPIP for tert-butylperoxyisopropylcarbonate (the above three being radical polymerizationinitiators), and “SP of polymer” for the value of the solubilityparameter of the polymer of the vinyl monomer (B-4) as determined by themethod described herein.

REFERENCE EXAMPLES 13 TO 15

Graft copolymers (SG′-1 to 3) each in a powder form were obtained in thesame manner as in Reference Example 7 except that the vinyl-based seedparticle (Sv-1) latex specified in Table 2 was used in lieu of thepolyorganosiloxane particle (B-1) latex used in Reference Example 7,that the monomer (B-3) mixture and monomer (B-4) mixture used were asspecified in Table 2, and that 0.1 part of sodiumdodecylbenzenesulfonate (15% aqueous solution) was added at 2-hourintervals during dropwise addition of the monomer (B-4) mixture. InReference Examples 14 and 15, the addition of the monomer (B-3) mixturewas omitted and the monomer (B-4) mixture alone was added. For eachReference Example, the conversion of monomers and the acetone insolublematter content are shown in Table 2.

REFERENCE EXAMPLE 16

A graft copolymer (SG′-4) was obtained in the same manner as inReference Example 7 except that the vinyl-based seed particle (Sv-1)latex specified in Table 2 was used in lieu of the polyorganosiloxaneparticle (B-1) latex used in Reference Example 7, that the monomer (B-3)mixture and monomer (B-4) mixture used were as specified in Table 2, andthat 0.1 part of sodium dodecylbenzenesulfonate (15% aqueous solution)was added at 2-hour intervals during dropwise addition of the monomer(B-3) mixture. The conversion of monomers and the acetone insolublematter content are shown in Table 2.

REFERENCE EXAMPLE 17

A graft copolymer (SG′-5) was obtained in the same manner as inReference Example 13 except that 0.5 part of sodiumdodecylbenzenesulfonate (20% aqueous solution) was used in lieu of thevinyl-based seed particle (Sv-1) latex used in Reference Example 13 andthat the monomer (B-3) mixture and monomer (B-4) mixture were asspecified in Table 2. The conversion of monomers and the acetoneinsoluble matter content are shown in Table 2.

REFERENCE EXAMPLE 18

A graft copolymer (SG′-6) was obtained in the same manner as inReference Example 16 except that 0.5 part of sodiumdodecylbenzenesulfonate (20% aqueous solution) was used in lieu of thevinyl-based seed particle (Sv-1) latex used in Reference Example 16 andthat the monomer (B-3) mixture and monomer (B-4) mixture were asspecified in Table 2. The conversion of monomers and the acetoneinsoluble matter content are shown in Table 2.

REFERENCE EXAMPLE 19

A graft copolymer (SG′-7) was obtained in the same manner as inReference Example 10 except that the same latex as thepolyorganosiloxane-containing graft copolymer (SG-7) obtained inReference Example 10 and that, on the isolation of graft copolymer fromthe latex, the coagulation with an aqueous solution of calcium chloridewas not carried out but the spray drying method was carried out forisolation. The conversion of monomers and the acetone insoluble mattercontent of SG′-7 are shown in Table 2.

REFERENCE EXAMPLE 20

A graft copolymer (SG-10) was obtained in the same manner as inReference Example 19 except that, in carrying out the spray dryingmethod for isolation, 1 part (on the solid basis) of an aqueousdispersion of calcium dodecylbenzenesulfonate as prepared by addingdropwise a 10% aqueous solution of dodecylbenzenesulfonic acid (softtype) (product of Tokyo Kasei Kogyo) to a 10% aqueous dispersion ofcalcium hydroxide (product of Wako Pure Chemical Industries)to therebyadjust the pH to 4 was introduced into a spray drier separately from thelatex and mixed drying was carried out in the spray drier. Theconversion of monomers and the acetone insoluble matter content of SG-10are shown in Table 2.

EXAMPLES 1 TO 9 AND COMPARATIVE EXAMPLES 1 TO 6 Rendering aPolycarbonate Resin Flame-Retardant

Using a polycarbonate resin (PC-1: Toughlon FN1900A, product of IdemitsuPetrochemical) and the polyorganosiloxane-containing graft copolymers(SG-1 to 9) obtained in Reference Examples 4 to 12 or the graftcopolymers (SG′-1 to 6) obtained in Reference Examples 13 to 18,compositions were prepared according to the formulations shown in Table3. Sodium dodecylbenzenesulfonate was used in the following manner: a 2%aqueous solution thereof was preliminarily incorporated in thepolyorganosiloxane-containing graft copolymers (SG-1 to 9) or graftcopolymers (SG′-1 to 6) in powder form according to the formulationsshown in Table 3, followed by drying. The amounts of calciumdodecylbenzenesulfonate as shown in Table 3 are the values calculated onthe assumption that the whole amounts of sodium dodecylbenzenesulfonateused as the emulsifier in the production of thepolyorganosiloxane-containing graft copolymers (SG-1 to 9) or graftcopolymers (SG′-1 to 6) had been converted to the calcium salt.

Each composition obtained was melt-kneaded at 270° C. in a twin-screwextruder (Japan Steel Works' TEX 44 SS) and pelletized. The pelletsobtained were molded into ⅛-inch Izod test specimens and 1/16-inch and1/20-inch test specimens for flame retardancy evaluation using FANUC'sFAS 100 B injection molding machine set at a cylinder temperature of300° C. The test specimens obtained were evaluated by the evaluationmethods described above. The results obtained are shown in Table 3.

TABLE 3 Example 1 2 3 4 5 6 7 8 (A) Thermoplastic PC-1 100  100  100 100  100  100  100  100  resin (parts) (B) SG-1  3 — — — — — — —Polyorganosiloxane- SG-2 —  3 — — — — — — containing graft SG-3 — —  3 —— — — — copolymer (parts) SG-4 — — —  3 — — — — SG-5 — — — —  3 — — —SG-6 — — — — —  3 — — SG-7 — — — — — —  3 — SG-8 — — — — — — —  3 SG-9 —— — — — — — — SG′-1 — — — — — — — — SG′-2 — — — — — — — — SG′-3 — — — —— — — — SG′-4 — — — — — — — — SG′-5 — — — — — — — — SG′-6 — — — — — — —— (C) Metal salt (parts) SDBS    0.01    0.01    0.01    0.01    0.01   0.01    0.01    0.01 CDBS    0.06    0.05    0.07    0.08    0.10   0.10    0.12    0.12 (D) Fluororesin PTFE    0.25    0.25    0.25   0.25    0.25    0.25    0.25    0.25 (parts) Flame 1/16 Totalcombustion 18 21  9 25 23 18 12 18 retardancy inch time (s) Dripping NoNo No No No No No No 1/20 Total combustion 39 49 32 48 48 42 29 40 inchtime (s) Dripping No No No No No No No No Impact resistance −10° C.(kJ/m²) 32 28 30 27 29 34 30 31 Example Comparative Example 9 1 2 3 4 56 (A) Thermoplastic PC-1 100  100  100  100  100  100  100  resin(parts) (B) SG-1 — — — — — — — Polyorganosiloxane- SG-2 — — — — — — —containing graft SG-3 — — — — — — — copolymer (parts) SG-4 — — — — — — —SG-5 — — — — — — — SG-6 — — — — — — — SG-7 — — — — — — — SG-8 — — — — —— — SG-9  3 — — — — — — SG′-1 —  3 — — — — — SG′-2 — —  3 — — — — SG′-3— — —  3 — — — SG′-4 — — — —  3 — — SG′-5 — — — — —  3 — SG′-6 — — — — ——  3 (C) Metal salt (parts) SDBS    0.01    0.01    0.01    0.01    0.01   0.01    0.01 CDBS    0.12    0.06    0.15    0.15    0.15    0.01   0.01 (D) Fluororesin PTFE    0.25    0.25    0.25    0.25    0.25   0.25    0.25 (parts) Flame 1/16 Total combustion 22 231  158  203 221  258  214  retardancy inch time (s) Dripping No Yes Yes Yes Yes YesYes 1/20 Total combustion 49 * * * * * * inch time (s) Dripping No YesYes Yes Yes Yes Yes Impact resistance −10° C. (kJ/m²) 29  6  6  4 28  530 *The moldings were not self-extinguishing but burnt out.

In the table, PTFE stands for polytetrafluoroethylene (Polyflon FA-500,product of Daikin Industries), SDBS for sodium dodecylbenzenesulfonate(Neopelex F-25, product of Kao Corp.), and CDBS for calciumdodecylbenzenesulfonate (resulting from conversion of the emulsifierused in the step of polymerization to the calcium salt).

EXAMPLES 10 TO 21 AND COMPARATIVE EXAMPLES 7 TO 9

Using polycarbonate resins (PC-1, PC-2: Toughlon FN 1700 A, product ofIdemitsu Petrochemical) and the polyorganosiloxane-containing graftcopolymer (SG-7) obtained in Reference Example 10, compositions wereprepared according to the formulations given in Table 4. Potassiumdodecylbenzenesulfonate was used in the following manner: a 10% aqueoussolution of dodecylbenzenesulfonic acid (soft type) (product of TokyoKasei Kogyo) was neutralized to pH=6.5 with a 10% aqueous solution ofpotassium hydroxide (product of Wako Pure Chemical Industries), theresulting solution was diluted to a 2% aqueous solution, and thisdilution was preliminarily incorporated in thepolyorganosiloxane-containing graft copolymer (SG-7) according to theformulation shown in Table 4, like the sodium dodecylbenzenesulfonate inExample 7, followed by drying. As for the calciumdodecylbenzenesulfonate, the whole amounts of sodiumdodecylbenzenesulfonate used as in the production of thepolyorganosiloxane-containing graft copolymers (SG-7) was considered tohave been converted to the calcium salt. In Example 20 alone, a powderof calcium dodecylbenzenesulfonate was separately prepared by addingdropwise a 10% aqueous solution of dodecylbenzenesulfonic acid (softtype) (product of Tokyo Kasei Kogyo) to a 10% aqueous dispersion ofcalcium hydroxide (product of Wako Pure Chemical Industries) and dryingthe resulting aqueous dispersion adjusted to pH=4, and 0.01 part of thepowder was further added (the total amount being given in Table 4).

Thereafter, the procedure of Example 7 was followed, and the testspecimens obtained were evaluated according to the evaluation methodsdescribed above. The results are shown in Table 4.

EXAMPLES 22 AND COMPARATIVE EXAMPLES 10

The same procedure as used in Example 10 was used except that thepolyorganosiloxane-containing graft copolymer (SG-10) obtained inReference Example 20 was used in lieu of thepolyorganosiloxane-containing graft copolymer (SG-7) used in Example 10,that neither sodium dodecylbenzenesulfonate nor calciumdodecylbenzenesulfonate was further added, that the amount of sodiumdodecylbenzenesulfonate used was estimated by calculating the sum of thesodium dodecylbenzenesulfonate used in the production of SG-10 and theproduct of neutralization of the dodecylbenzenesulfonic acid with sodiumhydroxide, that the calcium dodecylbenzenesulfonate used in spray dryingwas used as such, and that the formulations given in Table 5 wereemployed. In Comparative Example 10 alone, a master batch was preparedby adding 0.5 part (as solid) of a 5% aqueous solution of sodiumdodecylbenzenesulfonate to the polycarbonate resin PC-1 and drying themixture, and this was diluted with PC-1 to give the compositionspecified in Table 5. The results are shown in Table 5.

TABLE 4 Example 10 11 12 13 14 15 16 17 (A) Thermoplastic PC-1 100  —100  100  — — — 100  resin (parts) PC-2 — 100  — — 100  100  100  — (B)SG-7  3  3  1  8  3  3  3  3 Polyorganosiloxane- containing graftcopolymer (parts) (C) Metal salt (parts) PPFBS — — — —    0.01 — — —PDPSS — — — — —    0.01 — — SDBS    0.01    0.01    0.01    0.01 — — —   0.01 PDBS — — — — — —    0.01 — CDBS    0.12    0.12    0.04    0.31   0.12    0.12    0.12    0.12 (D) Fluororesin PTFE    0.25   0.2   0.25    0.25   0.2   0.2   0.2    0.25 (parts) (E) Antioxidant TDBHIC— — — — — — —   0.4 (parts) TMHBB — — — — — — —   0.4 DLTP — — — — — — —— Flame 1.6 mm Total combustion 18 21 20 16 19 25 24 12 retardancy time(s) Dripping No No No No No No No No 1.2 mm Total combustion 39 48 41 3842 50 49 28 time (s) Dripping No No No No No No No No Impact resistance−10° C. (kJ/m²) 32 28 25 38 30 28 26 27 Example Compar. Example 18 19 2021 7 8 9 (A) Thermoplastic PC-1 100  100  — — 100  100  100  resin(parts) PC-2 — — 100  100  — — — (B) SG-7  3  3  3  3 — 35  3Polyorganosiloxane- containing graft copolymer (parts) (C) Metal salt(parts) PPFBS — — — — — — — PDPSS — — — — — — — SDBS    0.01 — — —   0.01    0.01  7 PDBS — — — — — — — CDBS    0.12    0.12    0.13   0.12 —    1.34    0.12 (D) Fluororesin PTFE    0.25    0.25   0.2  0.2    0.25    0.25    0.25 (parts) (E) Antioxidant TDBHIC   0.4 — — —— — — (parts) TMHBB — — — — — — — DLTP   0.4 — — — — — — Flame 1.6 mmTotal combustion 15 41 54 80 25 108  ** retardancy time (s) Dripping NoNo No No No Yes ** 1.2 mm Total combustion 33 113  97 155  44 198  **time (s) Dripping No No Yes Yes Yes Yes ** Impact resistance −10° C.(kJ/m²) 23 34 24 24  7 39 ** **No moldings could be obtained due totanning of resin.

TABLE 5 Example 19 22 23 Compar. Ex. 10 (A) Thermoplastic PC-1 100  100 100  100  resin (parts) (B) Polyorganosiloxane- SG-7  3 — — — containinggraft SG-10 —  3  3 — copolymer (parts) (C) Metal salt (parts) PPFBS — —— — PDPSS — — — — SDBS —    0.12    0.12    0.12 PDBS — — — — CDBS   0.12    0.03    0.03 — (D) Fluororesin PTFE    0.25    0.25    0.25   0.25 (parts) (E) Antioxidant TDBHIC — —   0.4 — (parts) TMHBB — —  0.4 — DLTP — — — — Flame 1.6 mm Total combustion time (s) 41 16 10 20retardancy Dripping No No No No 1.2 mm Total combustion time (s) 113  3525 41 Dripping No No No Yes Impact resistance −10° C. (kJ/m²) 34 31 28 6

In the tables, PPFBS stands for potassium perfluorobutanesulfonic acid(Megafac F-114, product of Dainippon Ink and Chemicals), PDPSS forpotassium diphenyl sulfone-3-sulfonate (KSS, product of Seal SandsChemicals), PDBS for potassium dodecylbenzenesulfonate, CDBS for calciumdodecylbenzenesulfonate, TDBHIC fortris(3,5-di-tert-butyl-4-hydroxybenyl) isocyanurate (Adekastab AO-20,product of Asahi Denka), TMHBB for1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane (AdekastabAO-30, product of Asahi Denka), and DLTP for dilauryl thiodipropionate(DLTP “Yoshitomi”, product of Yoshitomi Fine Chemicals).

EXAMPLES 24 AND 25 AND COMPARATIVE EXAMPLES 11 AND 12

Polyorganosiloxane-containing graft copolymer compositions comprisingthe polyorganosiloxane-containing graft copolymers (SG-7, SG-10, SG′-7)and sodium dodecylbenzenesulfonate and/or calciumdodecylbenzenesulfonate were prepared in the same manner as in Examples7, 19 and 20. They were evaluated for anti-blocking property. Thesepolyorganosiloxane-containing graft copolymer compositions were alsoevaluated for flame retardancy and impact resistance in the same manneras in Example 7. The results obtained are shown in Table 6.

TABLE 6 Example Compar. Ex. 24 25 11 12 (B) Polyorganosiloxane- SG-7  3—  3 — containing graft SG-10 —  3 — — copolymer (parts) SG′-7 — — —  3(C) Metal salt (parts) SDBS    0.01    0.12 —    0.12 CDBS    0.12   0.03    0.12 — Flame 1.2 mm Total combustion time (s) 29 25 113  38retardancy Dripping No No No Yes Anti-blocking property Pass through a18- 96 78 96 32 mesh sieve Impact resistance −10° C. (kJ/m²) 30 28 34 27

From Tables 3 to 5, it is apparent that the flame-retardantthermoplastic resin compositions of the invention greatly improve theflame retardancy-impact resistance balance of polycarbonate resins. Inparticular, it is evident that even in the case of thin moldings (1.2-mmthick), which are hardly caused to manifest good flame retardancy by theprior art methods, the flame-retardant thermoplastic resin compositionsof the invention show good flame retardancy.

From Table 6, it is apparent that the flame retardants for thermoplasticresins as provided by the invention can provide the thermoplastic resinswith good flame retardancy and, further, are excellent in powdercharacteristics as represented by their anti-blocking property.

INDUSTRIAL APPLICABILITY

In accordance with the invention, flame-retardant thermoplastic resincompositions excellent in both flame retardancy and impact resistance,in particular capable of retaining good flame retardancy even in theform of thin moldings as well as flame retardants for thermoplasticresins which are excellent in flame retardancy-impact resistance balanceand in powder characteristics as well can be obtained.

1. A flame-retardant thermoplastic resin composition, which comprises:100 parts by weight of a thermoplastic resin (A), 0.1 to 30 parts byweight of a polyorganosiloxane-containing graft copolymer (B) obtainedby polymerizing, in at least one stage, monomer(s) (B-3) and a vinylmonomer (B-4) in the presence of polyorganosiloxane particles (B-1),wherein monomer(s) (B-3) comprises a polyfunctional monomer (B-2)containing at least two polymerizable unsaturated bonds within themolecule thereof, 0.0005 to 5 parts by weight of at least one metal salt(C) selected from the group consisting of alkali metal salts andbivalent or further polyvalent metal salts, and 0.05 to 2 parts byweight of a fluororesin (D), wherein the polyorganosiloxane-containinggraft copolymer (B) is produced by polymerizing, in at least one stage,1.5 to 10 parts by weight, per 100 parts by weight of the wholecopolymer, of monomer(s) (B-3) comprising 100 to 20% by weight of apolyfunctional monomer (B-2) containing at least two polymerizableunsaturated bonds within the molecule thereof and 0 to 80% by weight ofanother copolymerizable monomer (B-5) in the presence of 40 to 95 partsby weight of polyorganosiloxane particles (B-1) and furtherpolymerizing, in at least one stage, 5 to 50 parts by weight of a vinylmonomer (B-4).
 2. The flame-retardant thermoplastic resin compositionaccording to claim 1, wherein the thermoplastic resin (A) is apolycarbonate-based resin, the amount of thepolyorganosiloxane-containing graft copolymer (B) is 0.5 to 20 parts byweight per 100 parts by weight of the polycarbonate-based resin, themetal salt (C) is an alkali metal salt of a sulfur-containing organiccompound and/or a bivalent or further polyvalent metal salt of asulfur-containing organic compound and the amount thereof in total is0.001 to 5 parts by weight per 100 parts by weight of thepolycarbonate-based resin.
 3. The flame-retardant thermoplastic resincomposition according to claim 2, wherein the metal salt (C) comprisesboth an alkali metal salt of a sulfur-containing organic compound and abivalent or further polyvalent metal salt of a sulfur-containing organiccompound.
 4. The flame-retardant thermoplastic resin compositionaccording to claims 1 or 2, wherein the bivalent or further polyvalentmetal salt is an alkaline earth metal salt.
 5. The flame-retardantthermoplastic resin composition according to claim 1, wherein thepolyorganosiloxane-containing graft copolymer (B) is produced bypolymerizing, in at least one stage, 1.5 to 8 parts by weight, per 100parts by weight of the whole copolymer, of monomer(s) (B-3) comprising100 to 20% by weight of a polyfunctional monomer (B-2) containing atleast two polymerizable unsaturated bonds within the molecule thereofand 0 to 80% by weight of another copolymerizable monomer (B-5) in thepresence of 40 to 95 parts by weight of polyorganosiloxane particles(B-1) and further polymerizing, in at least one stage, 5 to 50 parts byweight of a vinyl monomer (B-4).
 6. The flame-retardant thermoplasticresin composition according to claims 1 or 2, wherein thepolyorganosiloxane particles (B-1) has a volume average particlediameter of 0.008 to 0.6 μm.
 7. The flame-retardant thermoplastic resincomposition according to claims 1 or 2, wherein the polyorganosiloxaneparticles (B-1) are produced without using any tri- or furtherpoly-functional silane.
 8. The flame-retardant thermoplastic resincomposition according to claims 1 or 2, wherein the polyorganosiloxaneparticles (B-1) are in a latex form.
 9. The flame-retardantthermoplastic resin composition according to claims 1 or 2, wherein thevinyl monomer (B-4) is such one that a polymer derived from that monomeralone has a solubility parameter of 9.15 to 10.15 (cal/cm³)^(1/2). 10.The flame-retardant thermoplastic resin composition according to claims1 or 2, wherein the vinyl monomer (B-4) is at least one monomer selectedfrom the group consisting of aromatic vinyl monomers, vinyl cyanidemonomers, (meth)acrylic ester monomers and carboxyl group-containingvinyl monomers.
 11. The flame-retardant thermoplastic resin compositionaccording to claims 2 or 3, wherein the sulfur-containing organiccompound is at least one compound selected from the group consisting ofsulfonamides, (alkyl)aromatic sulfonic acids, perfluoroalkanesulfonicacids, aliphatic sulfonic acids and diphenyl sulfone sulfonic acids. 12.The flame-retardant thermoplastic resin composition according to claim11, wherein the sulfur-containing organic compound is an (alkyl)aromaticsulfonic acid.
 13. The flame-retardant thermoplastic resin compositionaccording to claims 1 or 2, which further comprises not more than 2parts by weight of an antioxidant (E).
 14. The flame-retardantthermoplastic resin composition according to claim 13, wherein theantioxidant (E) comprises a combination of at least one antioxidanthaving the isocyanuric ring structure within the molecule thereof and atleast one other antioxidant.
 15. A flame retardant for thermoplasticresins, which comprises: a polyorganosiloxane-containing graft copolymer(B) obtained by polymerizing, in at least one stage, monomer(s) (B-3)and a vinyl monomer (B-4) in the presence of polyorganosiloxaneparticles (B-1), wherein monomer(s) (B-3) comprises a polyfunctionalmonomer (B-2) containing at least two polymerizable unsaturated bondswithin the molecule thereof, an alkali metal salt of a sulfur-containingorganic compound, and a bivalent or further polyvalent metal salt of asulfur-containing organic compound, wherein thepolyorganosiloxane-containing graft copolymer (B) is produced bypolymerizing, in at least one stage, 1.5 to 10 parts by weight, per 100parts by weight of the whole copolymer, of monomer(s) (B-3) comprising100 to 20% by weight of a polyfunctional monomer (B-2) containing atleast two polymerizable unsaturated bonds within the molecule thereofand 0 to 80% by weight of another copolymerizable monomer (B-5) in thepresence of 40 to 95 parts by weight of polyorganosiloxane particles(B-1) and further polymerizing, in at least one stage, 5 to 50 parts byweight of a vinyl monomer (B-4).
 16. The flame-retardant forthermoplastic resins according to claim 15, wherein thepolyorganosiloxane-containing graft copolymer (B) is produced bypolymerizing, in at least one stage, 1.5 to 8 parts by weight, per 100parts by weight of the whole copolymer, of monomer(s) (B-3) comprising100 to 20% by weight of a polyfunctional monomer (B-2) containing atleast two polymerizable unsaturated bonds within the molecule thereofand 0 to 80% by weight of another copolymerizable monomer (B-5) in thepresence of 40 to 95 parts by weight of polyorganosiloxane particles(B-1) and further polymerizing, in at least one stage, 5 to 50 parts byweight of a vinyl monomer (B-4).
 17. A method of producingflame-retardant thermoplastic resin composition, which comprises;emulsion-polymerizing, in at least one stage, monomer(s) (B-3) and/or avinyl monomer (B-4) in the presence of polyorganosiloxane particles(B-1), wherein monomer(s) (B-3) comprises a polyfunctional monomer (B-2)containing at least two polymerizable unsaturated bonds within themolecule thereof, recovering the resulting polyorganosiloxane-containinggraft copolymer containing a bivalent or further polyvalent metal saltof a sulfur-containing organic compound by the coagulation method,adding a thermoplastic resin (A), an alkali metal salt of asulfur-containing organic compound, and a fluororesin (D) to thepolyorganosiloxane-containing graft copolymer containing the bivalent orfurther polyvalent metal salt of the sulfur-containing organic compound,and melt-kneading the mixture.
 18. A method of producing flame retardantfor thermoplastic resins, which comprises: emulsion-polymerizing, in atleast one stage, monomer(s) (B-3) and/or a vinyl monomer (B-4) in thepresence of polyorganosiloxane particles (B-1), wherein monomer(s) (B-3)comprises a polyfunctional monomer (B-2) containing at least twopolymerizable unsaturated bonds within the molecule thereof, recoveringthe polyorganosiloxane-containing graft copolymer containing a bivalentor further polyvalent metal salt of a sulfur-containing organic compoundby the coagulation method, adding an alkali metal salt of asulfur-containing organic compound to the polyorganosiloxane-containinggraft copolymer containing the bivalent or further polyvalent metal saltof the sulfur-containing organic compound, and blending them.
 19. Themethod according to claims 17 or 18, wherein thepolyorganosiloxane-containing graft copolymer (B) is produced bypolymerizing, in at least one stage, 1.5 to 10 parts by weight, per 100parts by weight of the whole copolymer, of monomer(s) (B-3) comprising100 to 20% by weight of a polyfunctional monomer (B-2) containing atleast two polymerizable unsaturated bonds within the molecule thereofand 0 to 80% by weight of another copolymerizable monomer (B-5) in thepresence of 40 to 95 parts by weight of polyorganosiloxane particles(B-1) and further polymerizing, in at least one stage, 5 to 50 parts byweight of a vinyl monomer (B-4).